[英]How do I replace a string variable with a var in Roslyn?
对于本地声明,例如:string a = string.Empty;
如何编写诊断程序以将其更改为:var a = string.Empty;
你不能。 var关键字告诉编译器执行类型推断,并且只使用var a;
编译器没有足够的信息来推断类型。
但是,您可以执行以下任何操作
var a = new String();
var b = String.Empty;
var c = "";
但这似乎比它的价值更多的努力。
编辑更新的请求:为什么要修改要使用var声明的所有代码? 无论如何,它编译为相同的IL(简单的例子):
// var a = String.Empty;
IL_0000: ldsfld string [mscorlib]System.String::Empty
IL_0005: pop
// string b = String.Empty;
IL_0006: ldsfld string [mscorlib]System.String::Empty
IL_000b: pop
我已经整理了一个带诊断的代码修复程序。 这是有趣的部分:
从ISyntaxNodeAnalyzer实现AnalyzeNode
public void AnalyzeNode(SyntaxNode node, SemanticModel semanticModel, Action<Diagnostic> public void AnalyzeNode(SyntaxNode node, SemanticModel semanticModel, Action<Diagnostic> addDiagnostic, CancellationToken cancellationToken)
{
var localDeclaration = (LocalDeclarationStatementSyntax)node;
if (localDeclaration.Declaration.Type.IsVar) return;
var variable = localDeclaration.Declaration.Variables.First();
var initialiser = variable.Initializer;
if (initialiser == null) return;
var variableTypeName = localDeclaration.Declaration.Type;
var variableType = semanticModel.GetTypeInfo(variableTypeName).ConvertedType;
var initialiserInfo = semanticModel.GetTypeInfo(variable.Initializer.Value);
var typeOfRightHandSideOfDeclaration = initialiserInfo.Type;
if (Equals(variableType, typeOfRightHandSideOfDeclaration))
{
addDiagnostic(Diagnostic.Create(Rule, node.GetLocation(), localDeclaration.Declaration.Variables.First().Identifier.Value));
}
}
这主要是查看声明两侧的类型,如果它们相同(并且RHS不是var),则添加诊断。
这是代码修复的代码:
public async Task<IEnumerable<CodeAction>> GetFixesAsync(Document document, TextSpan span, IEnumerable<Diagnostic> diagnostics, CancellationToken cancellationToken)
{
var root = await document.GetSyntaxRootAsync(cancellationToken).ConfigureAwait(false);
var diagnosticSpan = diagnostics.First().Location.SourceSpan;
var declaration = root.FindToken(diagnosticSpan.Start).Parent.AncestorsAndSelf().OfType<LocalDeclarationStatementSyntax>().First();
return new[] { CodeAction.Create("Use var", c => ChangeDeclarationToVar(document, declaration, c)) };
}
private async Task<Document> ChangeDeclarationToVar(Document document, LocalDeclarationStatementSyntax localDeclaration, CancellationToken cancellationToken)
{
var root = await document.GetSyntaxRootAsync(cancellationToken);
var variableTypeName = localDeclaration.Declaration.Type;
var varTypeName = SyntaxFactory.IdentifierName("var").WithAdditionalAnnotations(Formatter.Annotation);
var newDeclaration = localDeclaration.ReplaceNode(variableTypeName, varTypeName);
var newRoot = root.ReplaceNode(localDeclaration, newDeclaration);
return document.WithSyntaxRoot(newRoot);
}
这一点很简单,只需从Syntax工厂获取var并将其切换出来。 请注意,var在SyntaxFactory中没有自己的静态方法,因此它是按名称引用的。
编译器无法从中推断出类型。
你需要使用:
var a = ""; // compiler can see that is type `string`:
或者你可以这样做:
string a;
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