Table of Contents

5.4.3.3 ReDim Statement

Note

This section describes the implementation of MS-VBAL §5.4.3.3 ReDim Statement.

Syntax

AST node Instruction kind(s) Notes
RedimDeclarationNode Simple One node per comma-separated ReDim target. The node is a declaration and a statement at once: it declares the name it may introduce, and it executes where it appears. Its Target is an expression: a SimpleNameExpressionNode (a), or a MemberAccessExpressionNode (obj.Buffer, Me.Buffer, .Buffer) with the owner as the expression it is.
RedimBoundsNode — The dimension clause of one target, holding one RedimDimensionNode per dimension.

See RD-VBAL §3.4.2 Simple Statements.

Static Semantics

ReDim may be used to declare a VBResizableArrayValue, or to redimension an already-declared VBResizableArrayValue. It is invalid to use ReDim with a VBFixedSizeArrayValue. See RD-VBAL §2.4.1 Intrinsic Types.

The target name of a ReDim statement decides what the statement is:

Target name The ReDim statement is
Resolves to a local, a parameter, or a module field A re-dimension of an existing array.
Unqualified, and resolves to nothing An implicit declaration.

For an implicit ReDim declaration:

ReDim bounds are ordinary run-time expressions, not constant expressions. A ReDim bound is therefore an expression node, and not the verbatim text a declared array bound keeps (RD-VBAL §5.4.3.1 Local Variable Declarations). ReDim Grid(1 To n) is legal, and n is not knowable before the statement runs.

A dimension declared without a lower bound has no lower-bound node. The effective lower bound is the module's Option Base (RD-VBAL §5.2.1 Option Directives), which is a run-time dial rather than something the statement wrote.

Runtime Semantics

ReDim evaluates each bound where the statement stands, then re-allocates the array.

Target Effect
A resizable array Re-dimensioned.
A Variant holding an array Re-dimensioned. The variable keeps storing a Variant.
A Variant holding nothing yet Becomes an array. The static rule admits a Variant target so that it can become an array, so the Empty a Variant starts as is not the error below.
A Variant holding anything else Runtime error 13, Type mismatch.

Each bound is Let-coerced to Integer, as any other subscript is. An upper bound below its lower bound is runtime error 9, Subscript out of range.

Without Preserve, every element of the re-dimensioned array is its element type's default value.

Preserve

Preserve keeps the elements that still fit. It may change the upper bound of the last dimension, and nothing else:

Change Result
The upper bound of the last dimension Allowed.
The upper bound of any other dimension Runtime error 9, Subscript out of range.
The lower bound of any dimension Runtime error 9, Subscript out of range.
The number of dimensions Runtime error 9, Subscript out of range.

An element the resized array has and the original did not is its element type's default value. An element at an index now outside the array's bounds is discarded.

A ReDim of a variable that is currently locked by a ByRef formal parameter is runtime error 10, This array is fixed or temporarily locked (MS-VBAL §5.4.3.3). An array passed by reference is its parameter's for as long as an activation on the call stack has one: another name for it - the module variable the argument is, a public variable of an object - cannot take its dimensions away. A ReDim of the parameter itself is not locked, which is what passing an array by reference is for; so is one of a parameter that is passed on down a chain of ByRef calls. The lock is the activation's, so it is gone once the call returns (ICallStackFrame.LocksAddress).

Note

MS-VBAL §5.4.3.4 states no such rule for Erase, and Erase does not raise error 10.

A target that is a member access (obj.Buffer, .Buffer) is an expression: the array is read from it, and the new array is written back through it, as an assignment to it is - the public variable of the object, or the field of the record. The element type of an array that has no dimensions yet is the one the member is declared with.

Implementation

Type or member Role
RedimDeclarationNode One ReDim target (RDCore.SDK).
RedimBoundsNode, RedimDimensionNode The dimension clause, as expression nodes (RDCore.SDK).
VBLocalVariableSymbol.DeclaredBy LocalDeclarationKind.ReDim marks a local introduced by an implicit ReDim declaration.
ModuleDirectives.Base The module's Option Base, which an omitted lower bound takes (RDCore.SDK).
RDCore.Runtime.Semantics.Statements.ArrayStatementRuntimeSemantics Evaluates the bounds and re-allocates the array; see RD-VBAL §3.5.4 Execution.

⏮️ RD-VBAL §5.4.3.2 Local Constant Declarations | ⏭️ RD-VBAL §5.4.3.4 Erase Statement

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