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---
name: abl-v10-learning
compatibility: opencode
completeness: 95
content-types:
- code
- guidance
- examples
- diagrams
description: '"Reference guide for Progress OpenEdge ABL 10.1A (2005) — data types"
variable declaration, procedures, functions, OOP basics, error handling, database
access, transaction handling, control flow'
license: MIT
maturity: stable
metadata:
domain: programming
output-format: code
related-skills: abl-v12-learning, algorithms
role: reference
scope: implementation
triggers: abl, abl programming, abl v10, openedge, openedge 10, progress 4gl, progress
abl
archetypes:
- educational
anti_triggers:
- brainstorming
- vague ideation
response_profile:
verbosity: medium
directive_strength: medium
abstraction_level: tactical
version: "1.0.0"
---
# Progress OpenEdge ABL 10.1A — Reference Guide
> **Version:** Progress OpenEdge 10.1A (December 2005)
> **Language:** ABL — Advanced Business Language (formerly Progress 4GL)
> **Purpose:** Comprehensive reference for developers working with OpenEdge v10 codebases.
---
## TL;DR Checklist
- [ ] `?` is the universal unknown/null value across all data types
- [ ] `INT64` does NOT exist in v10.1A — use `DECIMAL` for large integers
- [ ] `NO-UNDO` is recommended for most variables (faster, not rolled back on UNDO)
- [ ] `ERROR-STATUS` is reset on every `NO-ERROR` statement — check immediately
- [ ] No `CATCH`/`THROW`/`FINALLY` — only `ON ERROR`, `NO-ERROR`, `RETURN ERROR`
- [ ] `FOR EACH ... NO-LOCK` is required for read-only database access
- [ ] `UNDO, LEAVE` exits a transaction block with rollback
- [ ] `RELEASE` commits and releases locks immediately
- [ ] OOP exists but is limited — no `ENUM`, no `PACKAGE-PRIVATE`, no generic collections
- [ ] JSON support does NOT exist — use XML or temp-table READ-XML/WRITE-XML
---
## When to Use
Use this skill when:
- Working with legacy OpenEdge 10.1A (December 2005) codebases
- Maintaining or refactoring ABL procedures written for v10
- Migrating v10 code to later versions (v11, v12)
- Understanding ABL fundamentals: data types, variable declaration, procedures
- Learning the v10 error handling model (pre-CATCH/THROW)
- Understanding ABL's implicit transaction model
- Working with ABL's OOP constructs as they existed in v10
- Implementing database access patterns specific to v10
---
## When NOT to Use
Avoid this skill for:
- New development — use `programming-abl-v12-learning` for modern ABL
- Questions about `ENUM`, `VAR`, compound operators (`+=`, `-=`) — added in v12.3+
- JSON support — added in v11.x
- Generic collections (`List<T>`, `HashMap<K,V>`) — added in v12.5+
- Safe navigation operator (`?:`) — added in v12.5
- `CATCH`/`THROW`/`FINALLY` — added in v10.2B
---
## Core Reference Content
### Data Types in v10.1A
| Data Type | v10 | Range / Notes |
|-----------|:---:|---------------|
| `CHARACTER` | ✅ | Max 32,767 bytes. Default `""`. General-purpose string. |
| `LONGCHAR` | ✅ | Up to 2 GB − 1 byte. Code-page aware. For large text. Added v10.0B. |
| `INTEGER` | ✅ | 32-bit signed: −2,147,483,648 to +2,147,483,647. Default `0`. |
| `INT64` | ❌ | **Not in v10.1A.** Added in v10.1B. Use `DECIMAL` for large integers. |
| `DECIMAL` | ✅ | Up to 50 significant digits, up to 10 decimal places. Default `0`. |
| `LOGICAL` | ✅ | TRUE/YES / FALSE/NO / Unknown (`?`). Default `NO`. |
| `DATE` | ✅ | 1/1/32768 BC to 12/31/32767 AD. Default `?`. |
| `DATETIME` | ✅ | DATE + milliseconds from midnight. Local time. Default `?`. Added v10.0B. |
| `DATETIME-TZ` | ✅ | DATETIME + UTC offset in minutes. Stored in UTC. Default `?`. Added v10.0B. |
| `RAW` | ✅ | Binary data, ≤ 32K bytes. |
| `MEMPTR` | ✅ | In-memory binary buffer, up to 2 GB − 1 byte. Requires explicit allocation. |
| `ROWID` | ✅ | Unique opaque database record identifier. Preferred over RECID. |
| `RECID` | ✅ | Legacy 32-bit integer record ID. Use ROWID instead in new code. |
| `HANDLE` | ✅ | Pointer to any ABL object or UI widget. Default `?`. |
| `WIDGET-HANDLE` | ✅ | Alias for HANDLE. Interchangeable in v10. |
| `COM-HANDLE` | ✅ | ActiveX/COM automation object reference. Windows only. |
| `BLOB` | ✅ | Binary Large Object. Database/temp-table fields only. Up to 1 GB. Added v10.0B. |
| `CLOB` | ✅ | Character Large Object. Database/temp-table fields only. Up to 1 GB. Added v10.0B. |
| `CLASS` | ✅ | Reference to a user-defined class instance. Default `?`. |
| `ENUM` | ❌ | **Not in v10.** Added in v12. Use INTEGER constants or CHARACTER literals instead. |
> ⚠️ **Critical:** `INT64` does **not exist** in v10.1A. Use `DECIMAL` for values that exceed 2,147,483,647. Assigning a large value to `INTEGER` causes a runtime overflow error.
### Data Type Examples
**CHARACTER and LONGCHAR:**
```abl
DEFINE VARIABLE cName AS CHARACTER NO-UNDO.
DEFINE VARIABLE cFullName AS CHARACTER NO-UNDO INITIAL "Unknown".
DEFINE VARIABLE lcDocument AS LONGCHAR NO-UNDO. /* for large text content */
cName = "John Smith".
lcDocument = "This is a very long text content that could be gigabytes...".
/* Case-insensitive by default */
IF cName = "john smith" THEN /* evaluates to TRUE */
MESSAGE "Names match (case-insensitive)" VIEW-AS ALERT-BOX.
/* CASE-SENSITIVE modifier */
DEFINE VARIABLE cSensitive AS CHARACTER CASE-SENSITIVE NO-UNDO.
```
**INTEGER and DECIMAL:**
```abl
DEFINE VARIABLE iCount AS INTEGER NO-UNDO INITIAL 0.
DEFINE VARIABLE dAmount AS DECIMAL NO-UNDO INITIAL 0.00.
/* v10 must use DECIMAL for large integers — no INT64 available */
DEFINE VARIABLE dBigNum AS DECIMAL NO-UNDO.
dBigNum = 5000000000. /* exceeds INTEGER max — must be DECIMAL in v10 */
/* INTEGER arithmetic */
iCount = iCount + 1.
/* DECIMAL formatting */
dAmount = 1234567.89.
MESSAGE STRING(dAmount, "->>,>>>,>>9.99") VIEW-AS ALERT-BOX.
/* Displays: 1,234,567.89 */
```
**LOGICAL:**
```abl
DEFINE VARIABLE lActive AS LOGICAL NO-UNDO INITIAL FALSE.
DEFINE VARIABLE lUnknown AS LOGICAL NO-UNDO. /* default: NO */
lActive = TRUE. /* or YES */
lUnknown = ?. /* unknown value */
/* All three states */
IF lActive = TRUE THEN MESSAGE "Active".
IF lActive = NO THEN MESSAGE "Inactive".
IF lActive = ? THEN MESSAGE "Unknown state".
/* Shorthand: IF lActive checks for TRUE */
IF lActive THEN MESSAGE "Active flag is set".
```
**DATE, DATETIME, DATETIME-TZ:**
```abl
DEFINE VARIABLE dOrderDate AS DATE NO-UNDO.
DEFINE VARIABLE dtTimestamp AS DATETIME NO-UNDO.
DEFINE VARIABLE dtzUtcTime AS DATETIME-TZ NO-UNDO.
dOrderDate = TODAY.
dtTimestamp = NOW. /* DATETIME-TZ — current time with tz offset */
dtzUtcTime = NOW.
/* Construct a specific date */
dOrderDate = DATE(12, 31, 2005). /* December 31, 2005 */
/* Extract components */
MESSAGE DAY(dOrderDate) VIEW-AS ALERT-BOX. /* 31 */
MESSAGE MONTH(dOrderDate) VIEW-AS ALERT-BOX. /* 12 */
MESSAGE YEAR(dOrderDate) VIEW-AS ALERT-BOX. /* 2005 */
/* Date arithmetic — add integer days */
dOrderDate = dOrderDate + 30. /* 30 days later */
dOrderDate = dOrderDate - 7. /* 7 days earlier */
/* ISO date formatting */
MESSAGE ISO-DATE(dtTimestamp) VIEW-AS ALERT-BOX.
```
**HANDLE and MEMPTR:**
```abl
DEFINE VARIABLE hQuery AS HANDLE NO-UNDO.
DEFINE VARIABLE mBlock AS MEMPTR NO-UNDO.
/* HANDLE — points to an ABL object */
CREATE QUERY hQuery.
/* ... use hQuery ... */
DELETE OBJECT hQuery.
/* MEMPTR — raw binary buffer */
SET-SIZE(mBlock) = 1024. /* allocate 1024 bytes */
PUT-BYTE(mBlock, 1) = 65. /* write ASCII 'A' at byte 1 */
MESSAGE GET-BYTE(mBlock, 1) VIEW-AS ALERT-BOX. /* 65 */
SET-SIZE(mBlock) = 0. /* free the memory */
```
### Variable Declaration
**Full DEFINE VARIABLE Syntax:**
```abl
DEFINE
{ [ [ NEW [ GLOBAL ] ] SHARED ] | [ PRIVATE | PROTECTED | PUBLIC ] }
VARIABLE variable-name
{ AS datatype
| AS [ CLASS ] { type-name }
| LIKE field }
[ NO-UNDO ]
[ INITIAL { constant | { [ constant [ , constant ] ... ] } } ]
[ FORMAT string ]
[ EXTENT [ expression ] ]
[ LABEL string ]
[ DECIMALS n ]
[ CASE-SENSITIVE ]
```
**NO-UNDO Explained:**
`NO-UNDO` tells the ABL Virtual Machine (AVM) **not to roll back** this variable's value when an `UNDO` statement executes. This is recommended for most variables:
- **Without NO-UNDO:** The AVM tracks the "before image" of the variable for potential rollback. This adds overhead.
- **With NO-UNDO:** The variable is excluded from transaction rollback. Faster and more predictable.
```abl
/* With NO-UNDO (recommended) — not rolled back on UNDO */
DEFINE VARIABLE iCounter AS INTEGER NO-UNDO.
/* Without NO-UNDO — value will be rolled back if block UNDOs */
DEFINE VARIABLE iRollback AS INTEGER.
/* Demonstration: iRollback gets rolled back, iCounter does not */
DO TRANSACTION:
iCounter = 100.
iRollback = 100.
UNDO, LEAVE. /* only iRollback reverts to 0 */
END.
MESSAGE "Counter: " iCounter VIEW-AS ALERT-BOX. /* 100 — not rolled back */
MESSAGE "Rollback: " iRollback VIEW-AS ALERT-BOX. /* 0 — was rolled back */
```
**INITIAL Value:**
```abl
/* Simple initial values */
DEFINE VARIABLE cStatus AS CHARACTER NO-UNDO INITIAL "ACTIVE".
DEFINE VARIABLE iRetry AS INTEGER NO-UNDO INITIAL 3.
DEFINE VARIABLE lEnabled AS LOGICAL NO-UNDO INITIAL TRUE.
DEFINE VARIABLE dRate AS DECIMAL NO-UNDO INITIAL 0.15.
/* Unknown (null) initial — the default for DATE, DATETIME, DATETIME-TZ */
DEFINE VARIABLE dStartDate AS DATE NO-UNDO INITIAL ?.
```
**EXTENT — Arrays:**
```abl
/* Fixed-size array */
DEFINE VARIABLE arrMonths AS CHARACTER EXTENT 12 NO-UNDO.
DEFINE VARIABLE arrScores AS INTEGER EXTENT 5 NO-UNDO INITIAL [100, 95, 88, 72, 60].
/* Assign by index (1-based) */
arrMonths[1] = "January".
arrMonths[2] = "February".
arrMonths[12] = "December".
/* Read by index */
MESSAGE arrMonths[1] VIEW-AS ALERT-BOX. /* January */
/* Indeterminate (dynamic) extent — size set later */
DEFINE VARIABLE arrDynamic AS CHARACTER EXTENT NO-UNDO.
EXTENT(arrDynamic) = 20. /* set size at runtime */
/* EXTENT() function returns array size */
DEFINE VARIABLE iSize AS INTEGER NO-UNDO.
iSize = EXTENT(arrMonths). /* 12 */
```
**LIKE Field:**
The `LIKE` option inherits FORMAT, LABEL, DECIMALS, and CASE-SENSITIVE from a database field:
```abl
/* Inherits all format attributes from the Customer.Name field */
DEFINE VARIABLE cCustName AS CHARACTER NO-UNDO LIKE Customer.Name.
/* Inherits format but overrides label */
DEFINE VARIABLE dBalance AS DECIMAL NO-UNDO LIKE Customer.Balance
LABEL "Current Balance".
```
### Procedures and Functions
**Internal PROCEDURE Syntax:**
Internal procedures are defined within the same `.p` file and called with `RUN`:
```abl
PROCEDURE validateCustomer:
DEFINE INPUT PARAMETER piCustNum AS INTEGER NO-UNDO.
DEFINE OUTPUT PARAMETER pcError AS CHARACTER NO-UNDO.
/* Guard clause — check preconditions immediately */
IF piCustNum <= 0 THEN DO:
pcError = "Customer number must be positive".
RETURN.
END.
FIND Customer WHERE Customer.CustNum = piCustNum NO-LOCK NO-ERROR.
IF NOT AVAILABLE Customer THEN DO:
pcError = "Customer " + STRING(piCustNum) + " not found".
RETURN.
END.
IF ERROR-STATUS:ERROR THEN DO:
pcError = "Database error: " + ERROR-STATUS:GET-MESSAGE(1).
RETURN.
END.
pcError = "". /* empty string means success */
END PROCEDURE.
```
**User-Defined FUNCTION Syntax:**
Functions must be declared (or forward-declared) before their first use:
```abl
/* Forward declaration — required when function body appears later in the file */
FUNCTION formatCurrency RETURNS CHARACTER (INPUT dAmount AS DECIMAL) FORWARD.
/* Function that calculates a discount tier */
FUNCTION getDiscountRate RETURNS DECIMAL (INPUT dBalance AS DECIMAL):
IF dBalance >= 50000 THEN RETURN 0.20.
IF dBalance >= 10000 THEN RETURN 0.10.
IF dBalance >= 5000 THEN RETURN 0.05.
RETURN 0.00.
END FUNCTION.
/* Implementation of forward-declared function */
FUNCTION formatCurrency RETURNS CHARACTER (INPUT dAmount AS DECIMAL):
IF dAmount = ? THEN RETURN "N/A".
RETURN "$" + STRING(dAmount, "->>,>>>,>>9.99").
END FUNCTION.
/* Usage */
DEFINE VARIABLE cFormatted AS CHARACTER NO-UNDO.
cFormatted = formatCurrency(INPUT 1234567.89).
MESSAGE cFormatted VIEW-AS ALERT-BOX. /* $1,234,567.89 */
```
**Parameter Modes:**
| Mode | Direction | Description |
|------|-----------|-------------|
| `INPUT` | Caller → Procedure | Read-only in called procedure |
| `OUTPUT` | Procedure → Caller | Caller provides uninitialized variable |
| `INPUT-OUTPUT` | Both directions | Caller provides value; procedure can modify it |
| `RETURN` | Procedure → Caller | Special return parameter |
| `BUFFER` | Reference | Passes a database buffer by reference |
| `TABLE` | By value or ref | Passes a temp-table |
| `TABLE-HANDLE` | Handle | Passes a dynamic temp-table handle |
| `DATASET` | By value or ref | Passes a ProDataSet |
| `DATASET-HANDLE` | Handle | Passes a dynamic ProDataSet handle |
```abl
/* All standard parameter modes */
PROCEDURE demonstrateParams:
DEFINE INPUT PARAMETER pcInput AS CHARACTER NO-UNDO.
DEFINE OUTPUT PARAMETER pcOutput AS INTEGER NO-UNDO.
DEFINE INPUT-OUTPUT PARAMETER pdInOut AS DECIMAL NO-UNDO.
DEFINE RETURN PARAMETER prReturn AS LOGICAL NO-UNDO.
/* Buffer parameter — passes actual DB buffer by reference */
DEFINE PARAMETER BUFFER bCust FOR Customer.
/* Temp-table parameters */
DEFINE INPUT PARAMETER TABLE FOR ttOrder.
DEFINE OUTPUT PARAMETER TABLE FOR ttResult APPEND.
DEFINE INPUT PARAMETER TABLE-HANDLE httDynamic.
/* Dataset parameters */
DEFINE INPUT PARAMETER DATASET FOR dsOrders.
DEFINE OUTPUT PARAMETER DATASET-HANDLE hdsResult.
pcOutput = LENGTH(pcInput).
pdInOut = pdInOut * 2.
RETURN TRUE.
END PROCEDURE.
```
### Object-Oriented Programming (v10)
OOP was formally introduced in v10. While powerful, it is more limited than the v12 model.
**CLASS Statement Syntax:**
```abl
/* Basic class structure */
CLASS class-type-name
[ INHERITS super-type-name ]
[ IMPLEMENTS interface1 [, interface2]... ]
[ USE-WIDGET-POOL ]
[ ABSTRACT | FINAL ]
[ SERIALIZABLE ]
:
/* Data members, properties, constructors, methods, events, destructor */
END CLASS.
```
**Full v10 class example:**
```abl
CLASS acme.BankAccount:
/* Private data members */
DEFINE PRIVATE VARIABLE dBalance AS DECIMAL NO-UNDO INITIAL 0.
DEFINE PRIVATE VARIABLE cAccountId AS CHARACTER NO-UNDO.
DEFINE PRIVATE VARIABLE cOwnerName AS CHARACTER NO-UNDO.
/* Public property */
DEFINE PUBLIC PROPERTY Balance AS DECIMAL NO-UNDO
GET():
RETURN dBalance.
END GET.
PRIVATE SET. /* read-only externally */
DEFINE PUBLIC PROPERTY AccountId AS CHARACTER NO-UNDO
GET. /* auto-property: AVM manages backing store */
PRIVATE SET.
/* Constructor */
CONSTRUCTOR PUBLIC BankAccount(INPUT pcOwner AS CHARACTER,
INPUT pcAccId AS CHARACTER):
cOwnerName = pcOwner.
cAccountId = pcAccId.
END CONSTRUCTOR.
/* Public method */
METHOD PUBLIC LOGICAL Deposit(INPUT pdAmount AS DECIMAL):
IF pdAmount <= 0 THEN
RETURN FALSE.
dBalance = dBalance + pdAmount.
RETURN TRUE.
END METHOD.
METHOD PUBLIC LOGICAL Withdraw(INPUT pdAmount AS DECIMAL):
IF pdAmount <= 0 THEN RETURN FALSE.
IF pdAmount > dBalance THEN RETURN FALSE.
dBalance = dBalance - pdAmount.
RETURN TRUE.
END METHOD.
/* Destructor — called on DELETE OBJECT */
DESTRUCTOR PUBLIC BankAccount():
/* cleanup resources if needed */
END DESTRUCTOR.
END CLASS.
```
**Using the class:**
```abl
DEFINE VARIABLE rAccount AS CLASS acme.BankAccount NO-UNDO.
rAccount = NEW acme.BankAccount("John Smith", "ACC-001").
IF rAccount:Deposit(1000.00) THEN
MESSAGE "Deposit successful. Balance: " rAccount:Balance
VIEW-AS ALERT-BOX.
IF NOT rAccount:Withdraw(5000.00) THEN
MESSAGE "Insufficient funds" VIEW-AS ALERT-BOX.
/* Clean up — explicit in v10 */
DELETE OBJECT rAccount.
```
**INTERFACE Syntax:**
```abl
INTERFACE acme.IPayable:
/* Property prototypes — no implementation */
DEFINE PUBLIC PROPERTY AccountId AS CHARACTER NO-UNDO
GET.
SET.
/* Method prototypes */
METHOD PUBLIC LOGICAL Deposit(INPUT pdAmount AS DECIMAL).
METHOD PUBLIC LOGICAL Withdraw(INPUT pdAmount AS DECIMAL).
METHOD PUBLIC DECIMAL GetBalance().
END INTERFACE.
```
**Rules for interfaces in v10:**
- All members are implicitly `PUBLIC`
- No `PRIVATE`, `STATIC`, or `ABSTRACT` on interface members
- No constructors, destructors, or storage
- A class can implement multiple interfaces: `IMPLEMENTS IFaceA, IFaceB`
- Interfaces can inherit from other interfaces: `INTERFACE ISavings INHERITS IPayable:`
**Inheritance — INHERITS (Single):**
ABL v10 supports **single inheritance** only. A class can inherit from one parent:
```abl
CLASS acme.SavingsAccount INHERITS acme.BankAccount:
DEFINE PRIVATE VARIABLE dInterestRate AS DECIMAL NO-UNDO INITIAL 0.035.
/* Override or extend constructor */
CONSTRUCTOR PUBLIC SavingsAccount(INPUT pcOwner AS CHARACTER,
INPUT pcAccId AS CHARACTER,
INPUT pdRate AS DECIMAL):
SUPER(pcOwner, pcAccId). /* call parent constructor */
dInterestRate = pdRate.
END CONSTRUCTOR.
/* Add new method not in parent */
METHOD PUBLIC VOID ApplyInterest():
DEFINE VARIABLE dInterest AS DECIMAL NO-UNDO.
dInterest = THIS-OBJECT:Balance * dInterestRate.
THIS-OBJECT:Deposit(dInterest).
END METHOD.
END CLASS.
```
**Access Modifiers in v10:**
| Modifier | v10 | Accessible From |
|----------|:---:|-----------------|
| `PRIVATE` | ✅ | Defining class only (all instances of the same class can access each other's privates) |
| `PROTECTED` | ✅ | Defining class + any subclass in the hierarchy |
| `PUBLIC` | ✅ | Anywhere with a valid object reference or type name |
| `PACKAGE-PRIVATE` | ❌ | **Not in v10** — added in v12.2 |
| `PACKAGE-PROTECTED` | ❌ | **Not in v10** — added in v12.2 |
**Default access by member type:**
| Member Type | Default Access |
|-------------|---------------|
| Data members (variables) | `PRIVATE` |
| Properties | `PUBLIC` |
| Methods | `PUBLIC` |
| Events | `PUBLIC` |
| Constructors | `PUBLIC` |
### Error Handling (v10 Model)
> ⚠️ **Critical:** v10.1A does **not** have `CATCH`, `THROW`, or `FINALLY`. Those structured exception handling constructs were introduced in v10.2B. This section covers the **only** error handling mechanisms available in v10.
**The Three v10 Error Mechanisms:**
1. `ON ERROR` phrase on blocks
2. `NO-ERROR` option on statements + `ERROR-STATUS` system handle
3. `RETURN ERROR` to propagate errors to callers
**ON ERROR Phrase on Blocks:**
The `ON ERROR` phrase attaches to any block statement (`DO`, `REPEAT`, `FOR EACH`):
```abl
/* ON ERROR UNDO, LEAVE — undo block and exit it on error */
DO ON ERROR UNDO, LEAVE:
FIND Customer WHERE Customer.CustNum = 1001 EXCLUSIVE-LOCK.
Customer.Balance = Customer.Balance + 500.
/* On error: undo the find/update and exit this DO block */
END.
/* ON ERROR UNDO, RETRY — undo and retry the current iteration */
REPEAT ON ERROR UNDO, RETRY:
PROMPT-FOR Customer.CustNum.
FIND Customer USING CustNum NO-ERROR.
IF NOT AVAILABLE Customer THEN NEXT.
DISPLAY Customer.Name Customer.Balance.
END.
/* ON ERROR UNDO, NEXT — undo and skip to next iteration */
FOR EACH Customer ON ERROR UNDO, NEXT:
ASSIGN Customer.LastUpdated = TODAY NO-ERROR.
IF ERROR-STATUS:ERROR THEN
DISPLAY "Failed to update: " Customer.CustNum.
END.
/* ON ERROR UNDO, RETURN ERROR — propagate to caller */
DO TRANSACTION ON ERROR UNDO, RETURN ERROR:
FIND Order WHERE Order.OrderNum = iNum EXCLUSIVE-LOCK.
Order.Status = "CLOSED".
END.
```
**NO-ERROR Option:**
`NO-ERROR` suppresses the error condition and stores error information in `ERROR-STATUS`:
```abl
/* NO-ERROR on FIND */
FIND FIRST Customer WHERE Customer.CustNum = 9999 NO-LOCK NO-ERROR.
IF ERROR-STATUS:ERROR THEN DO:
MESSAGE "Error finding customer: " ERROR-STATUS:GET-MESSAGE(1)
VIEW-AS ALERT-BOX.
RETURN.
END.
IF NOT AVAILABLE Customer THEN DO:
MESSAGE "Customer not found" VIEW-AS ALERT-BOX.
RETURN.
END.
/* NO-ERROR on ASSIGN */
ASSIGN Customer.Balance = dNewBalance NO-ERROR.
IF ERROR-STATUS:ERROR THEN DO:
MESSAGE "Assignment error: " ERROR-STATUS:GET-MESSAGE(1)
VIEW-AS ALERT-BOX.
UNDO, RETURN ERROR.
END.
/* NO-ERROR on RUN */
RUN validateOrder (INPUT iOrderNum, OUTPUT cError) NO-ERROR.
IF ERROR-STATUS:ERROR THEN
cError = ERROR-STATUS:GET-MESSAGE(1).
```
**ERROR-STATUS System Handle:**
`ERROR-STATUS` is a built-in system handle that contains information about the last error:
| Attribute / Method | Type | Description |
|-------------------|------|-------------|
| `ERROR-STATUS:ERROR` | LOGICAL | TRUE if the last `NO-ERROR` statement raised an error |
| `ERROR-STATUS:NUM-MESSAGES` | INTEGER | Count of error messages in the error stack |
| `ERROR-STATUS:GET-MESSAGE(n)` | CHARACTER | Error message text at index n (1-based) |
| `ERROR-STATUS:GET-NUMBER(n)` | INTEGER | Error number/code at index n (1-based) |
```abl
/* Check all messages in the error stack */
DEFINE VARIABLE ix AS INTEGER NO-UNDO.
FIND Customer WHERE Customer.CustNum = 9999 NO-LOCK NO-ERROR.
IF ERROR-STATUS:ERROR THEN DO:
DO ix = 1 TO ERROR-STATUS:NUM-MESSAGES:
MESSAGE "Error " ix ": [" ERROR-STATUS:GET-NUMBER(ix) "] "
ERROR-STATUS:GET-MESSAGE(ix)
VIEW-AS ALERT-BOX.
END.
END.
```
> ⚠️ **WARNING:** `ERROR-STATUS` is **reset on every `NO-ERROR` statement**. If you call two NO-ERROR statements in a row, only the second one's error info is preserved. Always check `ERROR-STATUS` immediately after the statement that could fail.
**❌ BAD — ERROR-STATUS may be reset by the second NO-ERROR:**
```abl
FIND Customer WHERE Customer.CustNum = 1 NO-LOCK NO-ERROR.
ASSIGN Customer.Balance = 500 NO-ERROR.
IF ERROR-STATUS:ERROR THEN /* This reflects only the ASSIGN, not the FIND */
MESSAGE "Error" VIEW-AS ALERT-BOX.
```
**✅ GOOD — Check immediately after each NO-ERROR statement:**
```abl
FIND Customer WHERE Customer.CustNum = 1 NO-LOCK NO-ERROR.
IF ERROR-STATUS:ERROR THEN DO:
MESSAGE "FIND error: " ERROR-STATUS:GET-MESSAGE(1) VIEW-AS ALERT-BOX.
RETURN.
END.
IF NOT AVAILABLE Customer THEN RETURN.
ASSIGN Customer.Balance = 500 NO-ERROR.
IF ERROR-STATUS:ERROR THEN DO:
MESSAGE "ASSIGN error: " ERROR-STATUS:GET-MESSAGE(1) VIEW-AS ALERT-BOX.
UNDO, RETURN ERROR.
END.
```
**v10 Combined Error + Transaction Pattern:**
The canonical v10 pattern for safe database updates:
```abl
/* Reliable v10 update pattern */
DEFINE VARIABLE lSuccess AS LOGICAL NO-UNDO.
lSuccess = FALSE.
DO TRANSACTION ON ERROR UNDO, LEAVE:
FIND Customer WHERE Customer.CustNum = iCustNum
EXCLUSIVE-LOCK NO-WAIT NO-ERROR.
IF ERROR-STATUS:ERROR THEN DO:
MESSAGE "Record locked or error: " ERROR-STATUS:GET-MESSAGE(1)
VIEW-AS ALERT-BOX.
UNDO, LEAVE.
END.
IF NOT AVAILABLE Customer THEN DO:
MESSAGE "Customer not found" VIEW-AS ALERT-BOX.
UNDO, LEAVE.
END.
ASSIGN
Customer.Balance = Customer.Balance + dAdjustment
Customer.LastUpdate = TODAY NO-ERROR.
IF ERROR-STATUS:ERROR THEN DO:
UNDO, LEAVE.
END.
lSuccess = TRUE.
END. /* transaction commits here if lSuccess = TRUE */
IF lSuccess THEN
MESSAGE "Update successful" VIEW-AS ALERT-BOX.
```
### Database Access
**FOR EACH Statement:**
The `FOR EACH` statement is ABL's primary record iteration construct:
```abl
/* Basic iteration — NO-LOCK is required for read-only access */
FOR EACH Customer NO-LOCK:
DISPLAY Customer.CustNum Customer.Name Customer.Balance.
END.
/* WHERE clause filtering */
FOR EACH Customer
WHERE Customer.Balance > 1000
AND Customer.Country = "USA"
NO-LOCK:
DISPLAY Customer.Name Customer.Balance.
END.
/* ORDER BY clause */
FOR EACH Customer
WHERE Customer.Country = "USA"
NO-LOCK
BY Customer.Name:
DISPLAY Customer.Name.
END.
/* Descending sort */
FOR EACH Customer
NO-LOCK
BY Customer.Balance DESCENDING:
DISPLAY Customer.Name Customer.Balance.
END.
/* Multi-table join */
FOR EACH Order NO-LOCK,
EACH OrderLine OF Order NO-LOCK,
FIRST Product OF OrderLine NO-LOCK:
DISPLAY Order.OrderNum OrderLine.Qty Product.Name.
END.
```
**BREAK BY and Accumulation:**
```abl
/* BREAK BY enables group processing and ACCUM functions */
FOR EACH Customer
NO-LOCK
BREAK BY Customer.State
BY Customer.Name:
/* Fires once at the start of each State group */
IF FIRST-OF(Customer.State) THEN
MESSAGE "=== State: " Customer.State " ===" VIEW-AS ALERT-BOX.
DISPLAY Customer.Name Customer.Balance.
/* Fires once at the end of each State group */
IF LAST-OF(Customer.State) THEN
DISPLAY "Subtotal for " Customer.State ":"
ACCUM SUM Customer.Balance.
END.
/* Accumulate function types: SUM, COUNT, MAX, MIN, AVERAGE */
FOR EACH OrderLine NO-LOCK BREAK BY OrderLine.OrderNum:
IF LAST-OF(OrderLine.OrderNum) THEN
DISPLAY "Order " OrderLine.OrderNum
" Lines: " ACCUM COUNT OrderLine.LineNum
" Total: " ACCUM SUM OrderLine.ExtPrice.
END.
```
**Lock Modes:**
| Lock Mode | Description |
|-----------|-------------|
| `NO-LOCK` | Read-only. No lock held. Other users can read and write. **Best for reports.** |
| `SHARE-LOCK` | Shared read lock. Others can share-lock but not exclusive-lock. |
| `EXCLUSIVE-LOCK` | Full write access. Other users must wait until the lock is released. |
| `NO-WAIT` | Do not block if lock unavailable — immediately return without the record. |
```abl
/* NO-LOCK — reporting and read-only */
FOR EACH Customer NO-LOCK:
DISPLAY Customer.Name.
END.
/* EXCLUSIVE-LOCK — for updates */
FIND Customer WHERE Customer.CustNum = 1001 EXCLUSIVE-LOCK NO-ERROR.
/* SHARE-LOCK — read with notification to others */
FIND Customer WHERE Customer.CustNum = 1001 SHARE-LOCK NO-ERROR.
/* NO-WAIT — try to lock but don't wait if unavailable */
FIND Customer WHERE Customer.CustNum = 1001 EXCLUSIVE-LOCK NO-WAIT NO-ERROR.
IF LOCKED(Customer) THEN
MESSAGE "Record is locked by another user" VIEW-AS ALERT-BOX.
/* Downgrade from EXCLUSIVE to NO-LOCK after update committed */
FIND CURRENT Customer NO-LOCK.
```
**FIND Statement:**
```abl
/* FIND FIRST — first record matching criteria */
FIND FIRST Customer WHERE Customer.Balance > 5000 NO-LOCK NO-ERROR.
IF NOT AVAILABLE Customer THEN
MESSAGE "No customers found" VIEW-AS ALERT-BOX.
/* FIND LAST — last record matching criteria */
FIND LAST Customer BY Customer.Balance DESCENDING NO-LOCK.
/* FIND using frame field value */
FIND Customer USING Customer.CustNum. /* matches frame input value */
/* FIND OF — uses index match to related table */
FOR EACH Order NO-LOCK:
FIND Customer OF Order NO-LOCK NO-ERROR.
IF AVAILABLE Customer THEN
DISPLAY Order.OrderNum Customer.Name.
END.
/* FIND CURRENT — reposition existing buffer (change lock) */
FIND FIRST Customer NO-LOCK.
/* ... check the record ... */
FIND CURRENT Customer EXCLUSIVE-LOCK. /* upgrade to exclusive for update */
Customer.Balance = Customer.Balance + 100.
FIND CURRENT Customer NO-LOCK. /* downgrade lock when done */
/* CAN-FIND — boolean check without loading record into buffer */
IF CAN-FIND(Customer WHERE Customer.CustNum = iNum) THEN
MESSAGE "Customer exists" VIEW-AS ALERT-BOX.
```
### Transaction Handling
**ABL Implicit Transaction Model:**
ABL uses an **implicit, scope-based transaction model**. There is no explicit `COMMIT` or `ROLLBACK` statement in the 4GL. Transactions are defined by block boundaries:
- **`REPEAT` block:** Each iteration is a separate transaction. The transaction commits at the bottom of each iteration or when `RELEASE` is called.
- **`DO TRANSACTION` block:** The entire `DO` block is one transaction. Commits at `END.` if no error occurred.
- **No block:** Without a transaction block, database writes create "chained" transactions that commit when the record buffer is released.
```abl
/* REPEAT — each iteration is auto-committed */
REPEAT:
CREATE Order.
Order.OrderNum = NEXT-VALUE(orderSeq).
Order.CustNum = iCustNum.
RELEASE Order. /* commits this iteration's transaction immediately */
END.
/* DO TRANSACTION — entire block is one atomic transaction */
DO TRANSACTION:
FIND Customer WHERE Customer.CustNum = 1001 EXCLUSIVE-LOCK.
ASSIGN
Customer.Balance = Customer.Balance + 500
Customer.LastUpdate = TODAY.
END. /* transaction commits here if no error */
/* Check if currently inside an active transaction */
IF TRANSACTION THEN
MESSAGE "Inside a transaction" VIEW-AS ALERT-BOX.
```
**UNDO Statement:**
```abl
/* Syntax */
UNDO [ label ] [ , action ]
/* Actions: RETRY, LEAVE, NEXT, RETURN ERROR */
/* UNDO, RETRY — undo current iteration and try again */
REPEAT ON ERROR UNDO, RETRY:
IF RETRY THEN MESSAGE "Retrying...".
FIND Customer WHERE Customer.CustNum = iNum EXCLUSIVE-LOCK NO-ERROR.
IF LOCKED(Customer) THEN DO:
PAUSE 1 NO-MESSAGE.
UNDO, RETRY. /* wait 1 second and retry the lock */
END.
/* ... proceed with update ... */
END.
/* UNDO, LEAVE — undo and exit the current block */
DO TRANSACTION ON ERROR UNDO, LEAVE:
FIND Order WHERE Order.OrderNum = iNum EXCLUSIVE-LOCK NO-ERROR.
IF NOT AVAILABLE Order THEN UNDO, LEAVE.
Order.Status = "PROCESSED".
END.
/* UNDO, NEXT — undo and skip to next iteration */
FOR EACH Customer EXCLUSIVE-LOCK ON ERROR UNDO, NEXT:
ASSIGN Customer.Balance = Customer.Balance * 1.05 NO-ERROR.
IF ERROR-STATUS:ERROR THEN
UNDO, NEXT.
END.
/* UNDO, RETURN ERROR — undo and signal error to caller */
PROCEDURE updateBalance:
DEFINE INPUT PARAMETER piCustNum AS INTEGER.
DEFINE INPUT PARAMETER pdAmount AS DECIMAL.
DO TRANSACTION ON ERROR UNDO, RETURN ERROR:
FIND Customer WHERE Customer.CustNum = piCustNum
EXCLUSIVE-LOCK NO-ERROR.
IF NOT AVAILABLE Customer THEN
UNDO, RETURN ERROR "Customer not found: " + STRING(piCustNum).
Customer.Balance = Customer.Balance + pdAmount.
END.
END PROCEDURE.
```
**RELEASE Statement:**
`RELEASE` commits the transaction and releases locks on a record buffer:
```abl
/* RELEASE frees the buffer and commits — same as reaching end of REPEAT iteration */
FOR EACH Order EXCLUSIVE-LOCK:
Order.Status = "PROCESSED".
RELEASE Order. /* commits the update and releases the lock immediately */
END.
```
### Control Flow
**IF / THEN / ELSE:**
```abl
/* Statement form — single action per branch */
IF Customer.Balance > 10000 THEN
MESSAGE "Gold customer" VIEW-AS ALERT-BOX.
ELSE IF Customer.Balance > 5000 THEN
MESSAGE "Silver customer" VIEW-AS ALERT-BOX.
ELSE
MESSAGE "Standard customer" VIEW-AS ALERT-BOX.
/* Block form — multiple actions per branch */
IF Customer.Balance > 10000 THEN DO:
ASSIGN Customer.Tier = "GOLD"
Customer.Discount = 0.15.
RUN notifyGoldStatus(INPUT Customer.CustNum).
END.
ELSE DO:
ASSIGN Customer.Tier = "STANDARD"
Customer.Discount = 0.00.
END.
```
**Inline IF Expression (Ternary):**
```abl
/* Inline IF evaluates to a value — like a ternary operator */
cTier = IF Customer.Balance > 10000 THEN "GOLD" ELSE "STANDARD".
dRate = IF lIsEmployee THEN 0.20 ELSE 0.10.
cStatus = IF lActive THEN "Active" ELSE "Inactive".
/* Can be nested */
cTier = IF Customer.Balance > 50000 THEN "PLATINUM"
ELSE IF Customer.Balance > 10000 THEN "GOLD"
ELSE IF Customer.Balance > 5000 THEN "SILVER"
ELSE "STANDARD".
```
**CASE Statement:**
```abl
/* Basic CASE */
CASE Customer.Tier:
WHEN "GOLD" THEN dDiscount = 0.15.
WHEN "SILVER" THEN dDiscount = 0.10.
WHEN "BRONZE" THEN dDiscount = 0.05.
OTHERWISE dDiscount = 0.00.
END CASE.
/* Multiple values per branch using OR WHEN */
CASE Order.Status:
WHEN "NEW" OR WHEN "PENDING" THEN DO:
MESSAGE "Order needs processing" VIEW-AS ALERT-BOX.
RUN queueOrder(INPUT Order.OrderNum).
END.
WHEN "SHIPPED" OR WHEN "DELIVERED" THEN
MESSAGE "Order is on its way" VIEW-AS ALERT-BOX.
WHEN "CANCELLED" THEN
RUN archiveOrder(INPUT Order.OrderNum).
OTHERWISE
MESSAGE "Unknown status: " Order.Status VIEW-AS ALERT-BOX.
END CASE.
```
**DO Loop:**
```abl
/* Counted loop */
DEFINE VARIABLE ix AS INTEGER NO-UNDO.
DO ix = 1 TO 10:
DISPLAY ix.
END.
/* Counted loop with step */
DO ix = 10 TO 1 BY -1: /* countdown */
DISPLAY ix.
END.
/* While loop */
DEFINE VARIABLE lContinue AS LOGICAL NO-UNDO INITIAL TRUE.
DO WHILE lContinue:
/* ... do work ... */
IF iCount >= 100 THEN lContinue = FALSE.
END.
/* Transaction block */
DO TRANSACTION:
CREATE Customer.
Customer.CustNum = NEXT-VALUE(custSeq).
END.
/* Error-handling block */
DO ON ERROR UNDO, LEAVE:
FIND Customer WHERE Customer.CustNum = 9999 EXCLUSIVE-LOCK NO-ERROR.
IF NOT AVAILABLE Customer THEN LEAVE.
Customer.Balance = 0.
END.
```
**REPEAT Statement:**
```abl
/* Infinite loop — exits via LEAVE or RETURN */
REPEAT:
PROMPT-FOR Customer.CustNum.
FIND Customer USING Customer.CustNum NO-LOCK NO-ERROR.
IF NOT AVAILABLE Customer THEN DO:
MESSAGE "Customer not found. Try again." VIEW-AS ALERT-BOX.
NEXT.
END.
DISPLAY Customer.Name Customer.Balance.
LEAVE. /* exit after successful find */
END.
/* Counted REPEAT */
DEFINE VARIABLE ix AS INTEGER NO-UNDO.
REPEAT ix = 1 TO NUM-ALIASES:
MESSAGE ALIAS(ix) VIEW-AS ALERT-BOX.
END.
/* Transaction per iteration */
REPEAT TRANSACTION:
/* each pass through this loop is an auto-committed transaction */
CREATE Order.
Order.OrderNum = NEXT-VALUE(orderSeq).
/* ... */
RELEASE Order.
END.
```
**Named Blocks and LEAVE/NEXT:**
```abl
/* Named blocks allow LEAVE and NEXT to target specific blocks */
outerLoop:
DO ix = 1 TO 100:
innerLoop:
DO iy = 1 TO 100:
IF ix = 50 AND iy = 50 THEN
LEAVE outerLoop. /* exit the outer DO */
IF iy = 30 THEN
NEXT outerLoop. /* skip to next outer iteration */
END. /* innerLoop */
END. /* outerLoop */
```
**LEAVE, NEXT, RETURN:**
```abl
LEAVE. /* exit innermost block (like break in other languages) */
LEAVE blockLabel. /* exit named block */
NEXT. /* skip to next iteration (like continue) */
NEXT blockLabel. /* skip to next in named block */
RETURN. /* exit procedure/function normally */
RETURN "value". /* return a string value — accessible via RETURN-VALUE */
RETURN ERROR. /* exit and raise error condition in caller */
RETURN ERROR "message". /* exit with error message string */
```
---
## What v10 Does NOT Have
This section is critical for developers working with v10 code or migrating to a later version.
### Missing Language Features Table
| Feature | Status in v10 | When Added |
|---------|:-------------:|------------|
| `INT64` data type | ❌ Not in v10.1A | v10.1B |
| `ENUM` statement | ❌ | v12 |
| `VAR` shorthand declaration | ❌ | v12.3 |
| Compound operators (`+=`, `-=`, `*=`, `/=`) | ❌ | v12.3 |
| `CATCH` / `THROW` / `FINALLY` | ❌ | v10.2B |
| `BLOCK-LEVEL ON ERROR UNDO, THROW` directive | ❌ | Post-v10 |
| JSON support (`JsonObject`, `JsonArray`, `READ-JSON`, `WRITE-JSON`) | ❌ | v11.x |
| Generic collections (`List<T>`, `SortedSet<T>`, `HashMap<K,V>`) | ❌ | v12.5–12.7 |
| Safe navigation operator `?:` | ❌ | v12.5 |
| `PACKAGE-PRIVATE` access modifier | ❌ | v12.2 |
| `PACKAGE-PROTECTED` access modifier | ❌ | v12.2 |
| Override non-abstract properties | ❌ | v12.5 |
| `FINAL` on properties | ❌ | v12.5 |
| Server-side joins (FOR+NO-LOCK up to 10 tables) | ❌ | v12.0 |
| Class-based SAX callbacks (`EVENT-HANDLER-OBJECT`) | ❌ | v12 |
| `DYNAMIC-INVOKE()` for class methods | ⚠️ Limited | Improved v12 |
### How to Work Around Missing Features in v10
**Instead of INT64 — use DECIMAL:**
```abl
/* v10: no INT64 — use DECIMAL for large numbers */
DEFINE VARIABLE dBigCounter AS DECIMAL NO-UNDO.
dBigCounter = 9000000000. /* exceeds INTEGER max, fine as DECIMAL */
```
**Instead of ENUM — use INTEGER constants or CHARACTER literals:**
```abl
/* v10: no ENUM — use &DEFINE preprocessor constants */
&DEFINE STATUS_PENDING "PENDING"
&DEFINE STATUS_ACTIVE "ACTIVE"
&DEFINE STATUS_CLOSED "CLOSED"
/* Or use INTEGER constants */
&DEFINE ORDER_NEW 1
&DEFINE ORDER_PENDING 2
&DEFINE ORDER_SHIPPED 3
DEFINE VARIABLE iStatus AS INTEGER NO-UNDO INITIAL {&ORDER_NEW}.
IF iStatus = {&ORDER_SHIPPED} THEN
MESSAGE "Order shipped" VIEW-AS ALERT-BOX.
```
**Instead of CATCH/THROW — use NO-ERROR + ERROR-STATUS:**
```abl
/* v10: error handling without CATCH */
FIND Customer WHERE Customer.CustNum = iNum EXCLUSIVE-LOCK NO-ERROR.
IF ERROR-STATUS:ERROR THEN DO:
/* handle database error */
RETURN ERROR "DB error: " + ERROR-STATUS:GET-MESSAGE(1).
END.
IF NOT AVAILABLE Customer THEN DO:
RETURN ERROR "Customer not found: " + STRING(iNum).
END.
```
**Instead of generic collections — use comma-delimited strings or temp-tables:**
```abl
/* v10: simulate a list with a comma-delimited string */
DEFINE VARIABLE cGoldCustomers AS CHARACTER NO-UNDO.
FOR EACH Customer NO-LOCK WHERE Customer.Balance > 10000:
IF cGoldCustomers <> "" THEN
cGoldCustomers = cGoldCustomers + ",".
cGoldCustomers = cGoldCustomers + STRING(Customer.CustNum).
END.
/* Access items */
DEFINE VARIABLE ix AS INTEGER NO-UNDO.
DO ix = 1 TO NUM-ENTRIES(cGoldCustomers):
MESSAGE "Gold customer: " ENTRY(ix, cGoldCustomers) VIEW-AS ALERT-BOX.
END.
/* Or use a temp-table as a typed collection */
DEFINE TEMP-TABLE ttGoldCustomers NO-UNDO
FIELD CustNum AS INTEGER
FIELD Name AS CHARACTER
INDEX ixCustNum IS PRIMARY CustNum.
FOR EACH Customer NO-LOCK WHERE Customer.Balance > 10000:
CREATE ttGoldCustomers.
ASSIGN ttGoldCustomers.CustNum = Customer.CustNum
ttGoldCustomers.Name = Customer.Name.
END.
```
**Instead of safe navigation `?:` — use explicit VALID-OBJECT checks:**
```abl
/* v10: must check for null/invalid objects explicitly */
IF VALID-OBJECT(rOrder) THEN
IF VALID-OBJECT(rOrder:Customer) THEN
MESSAGE rOrder:Customer:Name VIEW-AS ALERT-BOX.
```
---
## Related Skills
| Skill | Purpose |
|-------|--------|
| `programming-abl-v12-learning` | Modern ABL (v12+) with ENUM, CATCH/THROW, JSON, generics |
| `programming-abl-v10-ui` | OpenEdge v10 UI patterns (frames, widgets, event handling) |
| `coding-code-review` | General code review methodology, OWASP security patterns |
---
## Version History Context
| Version | Release | Key Language Additions |
|---------|---------|----------------------|
| v10.0B | ~2005 | `DATETIME`, `DATETIME-TZ`, `BLOB`, `CLOB`, `LONGCHAR`, `NOW` |
| **v10.1A** | **Dec 2005** | **Formal OOP** (`CLASS`, `INTERFACE`, `METHOD`, events) |
| v10.1B | 2006 | `INT64` data type |
| v10.2B | ~2007 | `CATCH` / `THROW` / `FINALLY` structured error handling |
| v11.x | ~2011+ | JSON support (`JsonObject`, `JsonArray`, `READ-JSON`, `WRITE-JSON`) |
| v12.0 | 2019 | Server-side joins, STOP catchable by default, 64-bit sequences |
| v12.2 | 2020 | `PACKAGE-PRIVATE`, `PACKAGE-PROTECTED` |
| v12.3 | 2021 | `VAR` shorthand, compound operators (`+=`, `-=`), `CHAR`/`INT` synonyms |
| v12.5 | 2022 | Safe navigation `?:`, generic `List<T>`, override non-abstract properties |
| v12.7 | 2023 | `HashMap<K,V>`, `HASH-CODE`, signed archive libraries |
---
## Core Workflow
1. **Understand the Problem** — Identify inputs, outputs, constraints, and edge cases. **Checkpoint:** Clearly define the problem statement and expected behavior.
2. **Select Algorithm** — Choose the most appropriate algorithm based on constraints (time/space complexity, data size, ordering requirements). **Checkpoint:** Justify the algorithm choice with complexity analysis.
3. **Implement & Test** — Write clean, readable code with type hints, docstrings, and edge case handling. **Checkpoint:** Verify correctness with multiple test cases including edge cases.
4. **Analyze & Optimize** — Review time/space complexity, identify optimization opportunities, and validate against benchmarks. **Checkpoint:** Confirm complexity bounds match analysis and all test cases pass.
---
## Constraints
### MUST DO
- Include time and space complexity analysis for all algorithms
- Show at least one working example with input/output
- Include diagrams for non-trivial algorithm flows
### MUST NOT DO
- Present an algorithm without its complexity bounds
- Use recursive solutions without discussing tail-call or memoization alternatives
- Omit edge case handling in examples
## Live References
> Authoritative documentation links for this domain. The model follows markdown links at load time to resolve external references and inline content.
- [Introduction to Algorithms (CLRS)](https://mitpress.mit.edu/9780262046305/introduction-to-algorithms/) — Cormen, Leiserson, Rivest, Stein's definitive algorithms textbook with pseudocode and complexity analysis
- [Algorithms by Sedgewick & Wayne](https://algs4.cs.princeton.edu/home/) — Princeton's open-course algorithms textbook with Java implementations and visualizations
- [Algorithm Complexity Reference (Big-O Guide)](https://www.bigocheatsheet.com/) — Big-O complexity reference table for common algorithm operations and time/space trade-offs
- [LeetCode Problem Set](https://leetcode.com/) — LeetCode's curated collection of algorithm problems with community solutions and discussions
- [MIT OpenCourseWare: Analysis of Algorithms](https://ocw.mit.edu/courses/6-046j-introduction-to-algorithms-sma-5503-fall-2020/) — MIT's open course materials on algorithm design, analysis, and complexity theory
