Bind

Resolves a symbol referenced in an expression to an ITbExpression that produces its value.

Syntax: binder.Bind( symbol, argCount )

binder: required An object expression that evaluates to an ITbCustomBinder object.
symbol: required A String containing the name being looked up — the identifier as it appears in the source of the expression being compiled.
argCount: required A Long giving the number of arguments at the call site, or 0 if symbol is referenced as a bare value (a property-style access).

The return value is an ITbExpression whose Evaluate method produces the value of symbol when invoked, or Nothing to indicate that this binder cannot resolve symbol and the engine should fall through to the next binder.

Bind is called by the engine during compilation — once per unresolved symbol encountered in the expression source — not at evaluation time. The implementer is expected either to construct an ITbExpression that, when later evaluated, produces the value, or to return Nothing so that another binder gets a chance.

The argCount parameter lets the implementer distinguish a property-style reference (MyName, where argCount is 0) from a function-style call (MyName(1, 2, 3), where argCount is 3), and bind them to different things.

A class registers itself as a binder by including Implements ITbCustomBinder and then passing itself to AddCustomBinder.

Example

This ITbCustomBinder implementation looks up zero-argument symbols against the current row of an external recordset, deferring to the next binder for everything else.

Implements ITbCustomBinder

Public Recordset As Object

Protected Function Bind(ByVal Symbol As String, ByVal ArgCount As Long) As ITbExpression _
        Implements ITbCustomBinder.Bind

    If ArgCount = 0 AndAlso Recordset IsNot Nothing Then
        Dim Field As Object = Recordset.GetFieldBinder(Symbol)
        If TypeOf Field Is ITbExpression Then
            Return CType(Of ITbExpression)(Field)
        End If
    End If
    ' Returning Nothing lets the next binder try.
End Function

Bind

Example

See Also