5.4.3.9 Set Statement

Note

This section describes the implementation of MS-VBAL §5.4.3.9 Set Statement.

Syntax

AST node	Instruction kind(s)	Notes
AssignmentStatementNode (`Kind`: `Set`)	`Simple`	The same node type as `Let`, `LSet` and `RSet`, distinguished by `Kind`.

See RD-VBAL §3.4.2 Simple Statements.

Static Semantics

It is invalid for the default instance variable to be the target of a Set assignment, whatever is assigned to it (MS-VBAL §5.2.4.1.2 Default Instance Variables Static Semantics).

Statement, for a predeclared class `Widget`	Result
`Set Widget = New Widget`	Compile error `VBC09304`.
`Set Widget = Nothing`	Compile error `VBC09304`.
A `Set` assignment to a local variable or field that is itself named `Widget`	Valid. The local variable or field hides the default instance of class `Widget`, and is an ordinary `Set` target.

See RD-VBAL §3.1.1 Attributes (VB_PredeclaredId) and RD-VBAL §2.6.2 Semantic Compilation Errors.

Runtime Semantics

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

The value expression is evaluated.
The value is Set-coerced (MS-VBAL §5.5.2.2 Runtime semantics; RD-VBAL §5.5.2.2 Runtime semantics).
The Set-coerced value is assigned to the target.

Two things happen around the assignment of an object to a variable.

References. The variable holds a reference to the object it is given, and the object it held loses one. An object that loses its last reference is destroyed, and its Class_Terminate handler runs (RD-VBAL §5.3.1.10).
WithEvents. When the variable is declared WithEvents (RD-VBAL §5.2.3.1.2), its event handlers are detached from the object it holds before the assignment, and attached to the object it is given after it. They handle the events that object raises with RaiseEvent (RD-VBAL §5.4.2.20); an object that is destroyed handles no more.

Set obj.Member = value assigns a member as Let does (RD-VBAL §5.4.3.8), through the Property Set or the public variable, and with the same two things around it: the references and the WithEvents handlers are those of the object the variable belongs to.

The Set statement performs Set-coercion through the same direct entry point that RDCore.Runtime.Semantics.Statements.WithStatementRuntimeSemantics uses for its own With-target coercion, not through the operator pipeline. Set-coercion does not select a strategy per destination type, so it does not need the operator pipeline. Let-assignment, by contrast, reuses the operator pipeline; see RD-VBAL §5.4.3.8 Let Statement.

Implementation

Type or member	Role
`RDCore.Runtime.Semantics.Statements.StatementRuntimeSemanticsProvider`	Dispatches an `AssignmentStatementNode` whose `Kind` is `Set`.
ISetCoercionRuntimeSemantics`.EvaluateSetCoercion`	The direct Set-coercion entry point, shared with `WithStatementRuntimeSemantics`.