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How do I declare a var variable with Roslyn?

Tags:

c#

roslyn

I've got the following piece of code, but I can't find how to get the var TypeSyntax. Any ideas?

Syntax.LocalDeclarationStatement(                   
    declaration: Syntax.VariableDeclaration(
        type: Syntax.PredefinedType(Syntax.Token(SyntaxKind.VarKeyword)),
        variables: Syntax.SeparatedList(
        Syntax.VariableDeclarator(
            identifier: Syntax.Identifier(name)))
        )
    )
);

this fails with an Argument exception that says: "keyword"

like image 467
Sebastian Piu Avatar asked Dec 06 '11 12:12

Sebastian Piu


2 Answers

I'd use:

Syntax.LocalDeclarationStatement(
    declaration: Syntax.VariableDeclaration(
        type: Syntax.IdentifierName(Syntax.Token(SyntaxKind.VarKeyword)),
        variables: Syntax.SeparatedList(
            Syntax.VariableDeclarator(
                identifier: Syntax.Identifier(name)))));
like image 143
Jb Evain Avatar answered Sep 25 '22 19:09

Jb Evain


Jb Evain's answer is correct; I just thought that I would add that the reason for the error is because "var" is not a predefined type. A predefined type is something like "int" or "string".

The syntactic analyzer does not know whether or not you have a class named "var" in scope; "var" is treated not as a predefined type, but rather as just another name for just another type. Only if we cannot find a type in scope named "var" does the semantic analyzer then decide, oh, this must be an implicitly typed local.

The reason for this is because "var" was added in C# 3, and there might be C# 1 or 2 programs that use "var" as the name of a type. We did not want to break those programs.

like image 45
Eric Lippert Avatar answered Sep 22 '22 19:09

Eric Lippert