c# - 如何手动构建将始终返回 true 的表达式？

Question

我尝试创建表达式，但失败了。

我想构建类似 Expression<Func<typeof(type), bool>> expression = _ => true; 的东西

我的尝试:

private static Expression GetTrueExpression(Type type)
{
    LabelTarget returnTarget = Expression.Label(typeof(bool));
    ParameterExpression parameter = Expression.Parameter(type, "x");

    var resultExpression = 
      Expression.Return(returnTarget, Expression.Constant(true), typeof(bool));

    var delegateType = typeof(Func<,>).MakeGenericType(type, typeof(bool));

    return Expression.Lambda(delegateType, resultExpression, parameter); ;
}

用法:

var predicate = Expression.Lambda(GetTrueExpression(typeof(bool))).Compile();

但我收到错误:Cannot jump to undefined label ''

Answer 1

就这么简单:

private static Expression GetTrueExpression(Type type)
{
    return Expression.Lambda(Expression.Constant(true), Expression.Parameter(type, "_"));
}