C# CodeDom "as" 和 "is" 关键字功能

Question

Using CodeDom I'm looking for a way to generate c# code like this:

SomeRefType typedVar = obj as SomeRefType;

or this:

Boolean result = obj is SomeRefType;

But as far, all what I've found is CodeCastExpression class which can generate explicit type casting. But this is not what I need. Is there any way to implement "as" and "is" keywords functionality using CodeDom?

Answer 1

For history. Apparently, there's no universal way to implement these operators with CodeDom model.

It is possible to use CodeSnippetExpression to generate necessary code. But the solution becomes dependent on the target language used.

statements.Add(new CodeVariableDeclarationStatement("SomeRefType", "typedVar", new CodeSnippetExpression("obj as SomeRefType")));
statements.Add(new CodeVariableDeclarationStatement("Boolean", "result", new CodeSnippetExpression("obj is SomeRefType")));

Another option is to replace these operators with effectively similar logic. So for is operator the code is something like that:

statements.Add(new CodeVariableDeclarationStatement("Boolean", "result", new CodeMethodInvokeExpression(new CodeTypeOfExpression("SomeRefType"), "IsInstanceOfType", new CodeVariableReferenceExpression("obj"))));
// Boolean result = typeof(SomeRefType).IsInstanceOfType(obj);

and for as opeartor like that:

statements.Add(new CodeVariableDeclarationStatement("SomeRefType", "typedVal"));
statements.Add(new CodeConditionStatement(
    new CodeMethodInvokeExpression(new CodeTypeOfExpression("SomeRefType"), "IsInstanceOfType", new CodeVariableReferenceExpression("obj")),
    new CodeStatement[] { 
        new CodeAssignStatement(new CodeVariableReferenceExpression("typedVal"), new CodeCastExpression("SomeRefType", new CodeVariableReferenceExpression("obj")))
    },
    new CodeStatement[] {
        new CodeAssignStatement(new CodeVariableReferenceExpression("typedVal"), new CodePrimitiveExpression(null))
    }));
// SomeRefType typedVal = typeof(SomeRefType).IsInstanceOfType(obj) ? (SomeRefType)obj : null;

The generated IL-code is different from the code which is generated when using is and as operators. But in this case the target language can be any.