[英]Set parameter of any Func<>
I have an object of any of the func types func<>, Func<,>, func<,,>... And I'd like to replace one of the input parameters with a constant value.我有一个 object 的任何 func 类型 func<>, Func<,>, func<,,>... 我想用一个常量值替换其中一个输入参数。
eg:例如:
object SetParameter<T>(object function, int index, T value){
//I don't know how to code this.
}
Func<int, String, String> function = (a, b) => a.ToString() + b;
object objectFunction = function;
object newFunction = SetParameter<int>(objectFunction, 0, 5);
// Here the new function should be a Func<String, String> which value "(b) => function(5, b)"
I already now how to get the type of the resulting function, but that does not really help me in implementing the desired behavior:我现在已经如何获取生成的 function 的类型,但这并不能真正帮助我实现所需的行为:
private Type GetNewFunctionType<T>(object originalFunction, int index, T value)
{
Type genericType = originalFunction.GetType();
if (genericType.IsGenericType)
{
var types = genericType.GetGenericArguments().ToList();
types.RemoveAt(index);
Type genericTypeDefinition = genericType.GetGenericTypeDefinition();
return genericTypeDefinition.MakeGenericType(types.ToArray());
}
throw new InvalidOperationException($"{nameof(originalFunction)} must be a generic type");
}
It's not quite clear what the purpose of your conversion is for, but wouldn't it be easier to avoid all the reflection.目前尚不清楚转换的目的是什么,但避免所有反射不是更容易。 Eg:
例如:
Func<int, string, string> func3 = (a, b) => a.ToString() + b;
Func<string, string> func3withConst = (b) => func3(10, b);
Since you are talking about a very limited scope (supporting just Func<TReturn>
, Func<T1, TReturn>
and Func<T1, T2, TReturn>
) doing this through reflection is much more error prone and harder to read.由于您谈论的是非常有限的 scope (仅支持
Func<TReturn>
, Func<T1, TReturn>
和Func<T1, T2, TReturn>
)通过反射执行此操作更容易出错且更难阅读。
Just in case you need to use expression tree to build the function :以防万一您需要使用表达式树来构建 function :
object SetParameter<T>(object function, int index, T value)
{
var parameterTypes = function.GetType().GetGenericArguments();
// Skip where i == index
var newFuncParameterTypes = parameterTypes.SkipWhile((_, i) => i == index).ToArray();
// Let's assume function is Fun<,,> to make this example simple :)
var newFuncType = typeof(Func<,>).MakeGenericType(newFuncParameterTypes);
// Now build a new function using expression tree.
var methodCallParameterTypes = parameterTypes.Reverse().Skip(1).Reverse().ToArray();
var methodCallParameters = methodCallParameterTypes.Select(
(t, i) => i == index
? (Expression)Expression.Constant(value, typeof(T))
: Expression.Parameter(t, "b")
).ToArray();
// func.Invoke(5, b)
var callFunction = Expression.Invoke(
Expression.Constant(function),
methodCallParameters);
// b => func.Invoke(5, b)
var newFunc = Expression.Lambda(
newFuncType,
callFunction,
methodCallParameters.OfType<ParameterExpression>()
).Compile();
return newFunc;
}
To use this:要使用这个:
Func<int, string, string> func = (a, b) => a.ToString() + b;
var newFunc = (Func<string, string>)SetParameter<int>(func, 0, 5);
// Output: 5b
Console.WriteLine(newFunc("b"));
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