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Code blocks (CodeBlock)

{ |[parâmetros]| [expressão1, expressão2, ...] }

Create storable anonymous functions, receive parameters and evaluate expressions on demand with Eval().

CodeBlockCode blocksEvalAnonymous functionsExpressions

01 · OVERVIEW

Overview

A code block is an AdvPL value of type B (Block), similar to an anonymous function. It may receive parameters and execute one or more comma-separated expressions. Eval() executes the block and returns the result of its last expression. Unlike a regular function, its body accepts expressions and function calls, but not language commands.

02 · SYNTAX

Syntax

{ |[parâmetros]| [expressão1, expressão2, ...] }

Parameters

parâmetros

ListaOptional

Names between the vertical bars. They are local to the block and receive the supplied arguments.

expressões

AdvPLOptional

One or more comma-separated AdvPL expressions, executed from left to right.

retorno

QualquerOptional

The result of the last expression; an empty block returns NIL.

03 · PRACTICAL EXAMPLE

Simple block with a return value

User Function ExBlockSum()
    Local bAdd := { |nValue1, nValue2| Abs(nValue1) + Abs(nValue2) }
    Local nResult := Eval(bAdd, 10, -20)

    ConOut("Result: " + CValToChar(nResult))
Return

Expected result

Eval() supplies two arguments and receives 30, the result of the last expression.

04 · PRACTICAL EXAMPLE

Multiple expressions

User Function ExBlockList()
    Local bCalculate := { |nValue| ConOut("Received: " + CValToChar(nValue)), nValue * 2 }
    Local nResult := Eval(bCalculate, 5)

    MsgInfo("Double: " + CValToChar(nResult))
Return

Expected result

Expressions run from left to right and the return value is 10, the result of the last expression.

05 · PRACTICAL EXAMPLE

Custom sorting with ASort

User Function ExOrdenacao()
    Local aNomes := {"CARLA", "ANDREA", "BEATRIZ"}
    Local bDecrescente := { |cNome1, cNome2| cNome1 > cNome2 }

    ASort(aNomes, , , bDecrescente)
Return

Expected result

The block compares pairs selected by ASort() and enables descending order.

06 · PRACTICAL EXAMPLE

Pass by reference

User Function ExReferencia()
    Local bIncrementar := { |nValor| nValor += 1 }
    Local nContador := 0

    Eval(bIncrementar, nContador)  // nContador continua 0
    Eval(bIncrementar, @nContador) // nContador passa a 1
Return

Expected result

Without @, the block receives a copy; with @, its change reaches the original variable.

07 · PRACTICAL EXAMPLE

Capturing a local variable

User Function ExContexto()
    Local nContador := 0
    Local bSomar := { |nValor| nContador += nValor }

    Eval(bSomar, 5)
    ConOut("Contador: " + CValToChar(nContador))
Return

Expected result

The block references and changes nCounter in the Local context where it was created.

BEST PRACTICES

Braces delimit the block and two vertical bars delimit its parameter list, even when empty.
Block parameters have scope restricted to the block itself.
Eval(bBlock, arguments...) executes the content; @ passes a variable by reference.
Blocks are used for visual component events, sorting, evaluations and other APIs that receive behavior as an argument.
A block may capture a Local variable visible when it is created and retain that context while referenced.

COMMON PITFALLS

{ .T. } and { IIF(...) } are one-element arrays, not code blocks; they lack vertical bars.
Avoid large blocks: extract the logic into a function and let the block call it.
The official reference advises against calling a Static Function inside a block that may run from another source file because duplicate static names may cause indeterminate behavior.
Keeping a block that captured Local context for a long time may retain its memory area; remove references with NIL when no longer needed.
Follow the parameter count and return type expected by the function that evaluates the block.

Code blocks (CodeBlock)

Overview

Syntax

Parameters

Simple block with a return value

Multiple expressions

Custom sorting with ASort

Pass by reference

Capturing a local variable

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