C# 生成执行另一个表达式的表达式
我想构建一个使用另一个表达式的表达式,这将给我一个漂亮的C# 生成执行另一个表达式的表达式,c#,linq-expressions,C#,Linq Expressions,我想构建一个使用另一个表达式的表达式,这将给我一个漂亮的ToString()输出 用普通lambda表示,我想这样做: Func<string> extractFunc = () => "Marsh"; Func<bool> compareFunc = () => extractFunc() == "Mallow"; 我想要的是类似的东西: () => "March" == "Mallow" 我应该写什么来代替extractExp.Compile()
ToString()
输出
用普通lambda表示,我想这样做:
Func<string> extractFunc = () => "Marsh";
Func<bool> compareFunc = () => extractFunc() == "Mallow";
我想要的是类似的东西:
() => "March" == "Mallow"
我应该写什么来代替extractExp.Compile()()
(我可能不得不使用某种
ExpressionVisitor
来获得漂亮的输出。如果答案包括这一点,那就有好处了,但更重要的是如何将两个表达式
合并起来。)您在这里寻找的是一个组合
方法,它可以接受一个表达式并将其映射到一个接受相同输入的方法,但对第一个函数的结果执行操作:
public static Expression<Func<TResult>>
Compose<TIntermediate, TResult>(
this Expression<Func<TIntermediate>> first,
Expression<Func<TIntermediate, TResult>> second)
{
return Expression.Lambda<Func<TResult>>(
second.Body.Replace(second.Parameters[0], first.Body));
}
现在你可以写:
Expression<Func<string>> extractExp = () => "Marsh";
Expression<Func<bool>> compareExp = extractExp.Compose(s => s == "Mallow");
表达式extractExp=()=>“Marsh”;
表达式compareExp=extractExp.Compose(s=>s==“Mallow”);
public static Expression<Func<TResult>>
Compose<TIntermediate, TResult>(
this Expression<Func<TIntermediate>> first,
Expression<Func<TIntermediate, TResult>> second)
{
return Expression.Lambda<Func<TResult>>(
second.Body.Replace(second.Parameters[0], first.Body));
}
internal class ReplaceVisitor : ExpressionVisitor
{
private readonly Expression from, to;
public ReplaceVisitor(Expression from, Expression to)
{
this.from = from;
this.to = to;
}
public override Expression Visit(Expression node)
{
return node == from ? to : base.Visit(node);
}
}
public static Expression Replace(this Expression expression,
Expression searchEx, Expression replaceEx)
{
return new ReplaceVisitor(searchEx, replaceEx).Visit(expression);
}
Expression<Func<string>> extractExp = () => "Marsh";
Expression<Func<bool>> compareExp = extractExp.Compose(s => s == "Mallow");