Table of Contents

5.4.3.8 Let Statement

Note

This section describes the implementation of MS-VBAL §5.4.3.8 Let Statement.

Syntax

AST node Instruction kind(s) Notes
AssignmentStatementNode (Kind: ImplicitLet or ExplicitLet) Simple [Let] lExpression = expression. The Target of an AssignmentStatementNode is always an lExpression; see RD-VBAL §3.0.2 Node Types.

See RD-VBAL §3.4.2 Simple Statements.

Static Semantics

For a predeclared class Widget, Widget.Size = 3 is valid: it assigns a member of the object the default instance variable holds. See RD-VBAL §3.1.1 Attributes (VB_PredeclaredId).

Runtime Semantics

The executor dispatches a Let-assignment statement to its statement runtime semantics: Let-assignment is one of the statement kinds the Simple statement provider handles (RD-VBAL §3.5.4 Execution).

  1. StatementRuntimeSemanticsProvider.ExecuteLetAssignment evaluates the value expression.
  2. ExecuteLetAssignment passes the value to LetAssignmentEvaluator, which assigns it to the target:
Target Assignment
A bare reference to the procedure's own name, from within its own body Assigns the ReturnValue slot (the function result variable) instead of the general symbol table. The value is Let-coerced directly. See Function result variable.
A UDT field Let-coerces the value to the field's own declared type, and writes the field's cell. See UDT fields.
A variable Assigns through the "__let_op" Let-assignment operator: Let-assignment reuses the operator pipeline.

The Set statement does not use the operator pipeline; see RD-VBAL §5.4.3.9 Set Statement. Let-coercion is described in RD-VBAL §5.5.1.2 Runtime semantics.

Function result variable

A Let-assignment to a bare reference to a procedure's own name, from within its own body, assigns the ReturnValue slot instead of the general symbol table. See RD-VBAL §5.3.1.6 Subroutine and Function Declarations.

  • LetAssignmentEvaluator.Assign detects a self-reference the same way as RuntimeExpressionEvaluator.EvaluateSimpleName: by comparing the resolved symbol's Uri against RuntimeEvaluationContext.Scope. StatementRuntimeSemanticsProvider.ExecuteLetAssignment reaches it through LetAssignmentEvaluator.Assign.
  • A bare reference to the function result variable never goes through "__let_op". The function result variable is not an addressable Symbol with an IBindingHandle.
  • The self-reference branch of LetAssignmentEvaluator.Assign Let-coerces the assigned value directly.
  • That direct Let-coercion is the same lower-level call that ByVal and ByRef-fallback parameter passing make, for the same reason: there is no addressable symbol. See RD-VBAL §5.3.1.11 Procedure Invocation Argument Processing.

Members of an object

obj.Member = value assigns a member of the object obj holds (LetAssignmentEvaluator.AssignObjectMember). A Nothing reference raises error 91. The member is the Property Let declared for it (an indexed one takes the index arguments before the value) or else a public variable of the class, found through the declared interface when obj is declared as one its object's class implements (RD-VBAL §5.3.1.9). A public variable is assigned by Let-coercing the value to its declared type; with no such member, error 438 is raised. A With block assigns the same way.

Elements of an array

a(i, j) = value, and obj.Items(i) = value when the array is what a public variable of an object holds (LetAssignmentEvaluator.AssignArrayElement), assigns an element in place: the value is Let-coerced to the element type of the array and written to the element's own cell, and the array is never copied. A subscript outside the bounds of the array is error 9. Set a(i) = obj does the same with Set-coercion, and lets go of the object the element held and takes a reference to the one it is given.

A ReDim of an array gives it the element type of the variable's declaration (Dim a() As Long), including a variable of an object.

UDT fields

A Let statement assigns a UDT field by Let-coercing the value to the field's own declared type and writing the field's cell. It writes the cell because a UDT field is not an addressable symbol the way a variable is.

A UDT field is reachable from source code in both directions: a member access reads one, and a Let statement assigns one. See RD-VBAL §5.6.12 Member Access Expressions.

VBA copies a UDT on assignment. A copy of a UDT value gets a field store of its own, deep through a nested UDT; see RD-VBAL §2.5.2.1.3 User-Defined Type (UDT) Values.

Other statements that Let-assign

Statement Shares
For (ForOpener) Let-assigns the loop counter to start-value through the same Let-assignment machinery a Let statement uses. See RD-VBAL §5.4.2.3 For Statement.
Input #, Line Input #, Get Resolve their targets with LetAssignmentEvaluator.TryResolveTarget, the same target resolution the Let statement uses. See RD-VBAL §5.4.5 File Statements.

Implementation

Type or member Role
RDCore.Runtime.Semantics.Statements.StatementRuntimeSemanticsProvider.ExecuteLetAssignment Evaluates the value expression and passes it to LetAssignmentEvaluator.
RDCore.Runtime.Semantics.Statements.LetAssignmentEvaluator.Assign Assigns an evaluated value to the target: the function result variable, a UDT field, or a variable through "__let_op".
LetAssignmentEvaluator.TryResolveTarget Resolves the symbol a target names; shared with Input #, Line Input # and Get.
OperatorSymbolNames.BinaryAssignmentValueOp The name of the "__let_op" Let-assignment operator (RDCore.SDK).
ICallStackFrame.ReturnValue The function result variable.

⏮️ RD-VBAL §5.4.3.7 RSet Statement | ⏭️ RD-VBAL §5.4.3.9 Set Statement

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