Implementing an Expression Evaluator

Evaluating an expression is a complex interplay among the debug engine (DE), the symbol provider (SP), the binder object, and the expression evaluator (EE) itself. These four components are connected by interfaces that are implemented by one component and consumed by another.

The EE takes an expression from the DE in the form of a string and parses or evaluates it. The EE implements the following interfaces, which are consumed by the DE:

• IDebugExpressionEvaluator

• IDebugParsedExpression

The EE calls the binder object, supplied by the DE, to get the value of symbols and objects. The EE consumes the following interfaces, which are implemented by the DE:

• IDebugObject

• IDebugArrayObject

• IDebugFunctionObject

• IDebugPointerObject

• IDebugManagedObject

• IEnumDebugObjects

• IDebugBinder

The EE implements IDebugProperty2. IDebugProperty2 provides the mechanism for describing the result of an expression evaluation, such as a local variable, a primitive, or an object, to Visual Studio, which then displays the appropriate information in the Locals, Watch, or Immediate window.

The SP is given to the EE by the DE when it asks for information. The SP implements interfaces that describe addresses and fields, such as the following interfaces and their derivatives:

• IDebugSymbolProvider

• IDebugAddress

• IDebugField

The EE consumes all of these interfaces.

In This Section

• Expression Evaluator Implementation Strategy
  Defines a three-step process for the expression evaluator (EE) implementation strategy.

See Also

Other Resources

Writing a Common Language Runtime Expression Evaluator