Why is a URL Valid C#? - C#

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5 years ago Hosch250

This compiles because the http: part parses as a line label, and the //... part parses as a comment.

You can check the parse tree and confirm this at RoslynGenerator.

SyntaxFactory.LabeledStatement(
    identifier: SyntaxFactory.Identifier(
        leading: SyntaxFactory.TriviaList(SyntaxFactory.Whitespace("    ")),
        text: "https",
        trailing: default),
    colonToken: SyntaxFactory.Token(
        leading: default,
        kind: SyntaxKind.ColonToken,
        trailing: SyntaxFactory.TriviaList(
            SyntaxFactory.Comment("//topanswers.xyz/csharp"),
            SyntaxFactory.LineFeed)),
    statement: SyntaxFactory.ExpressionStatement(
        expression: SyntaxFactory.IdentifierName(
            identifier: SyntaxFactory.Identifier(
                leading: default,
                text: "",
                trailing: default)),
        semicolonToken: SyntaxFactory.Token(
            leading: default,
            kind: SyntaxKind.SemicolonToken,
            text: "",
            valueText: "",
            trailing: default)))

xxxxxxxxxx
 
SyntaxFactory.LabeledStatement(    identifier: SyntaxFactory.Identifier(        leading: SyntaxFactory.TriviaList(SyntaxFactory.Whitespace("    ")),        text: "https",        trailing: default),    colonToken: SyntaxFactory.Token(        leading: default,        kind: SyntaxKind.ColonToken,        trailing: SyntaxFactory.TriviaList(            SyntaxFactory.Comment("//topanswers.xyz/csharp"),            SyntaxFactory.LineFeed)),    statement: SyntaxFactory.ExpressionStatement(        expression: SyntaxFactory.IdentifierName(            identifier: SyntaxFactory.Identifier(                leading: default,                text: "",                trailing: default)),        semicolonToken: SyntaxFactory.Token(            leading: default,            kind: SyntaxKind.SemicolonToken,            text: "",            valueText: "",            trailing: default)))
show all 23 lines

The comment is part of the trailing trivia list on the colon token. If we had a statement, such as Console.WriteLine("Something..."); after the : token, that would be included in the statement node in the tree.

1 Answer