I read that C# lambdas can be imlicitly converted to Action or Func , but lambda cannot be executed directly Define a lambda function and execute it immediately For example :
int n = (()=>5)(); //doesn't work
int n = ((Func<int>)(()=>5))(); //works
So what is the actual type of lambda and why it cannot be directly called? Is it because C# type system is "weaker" than Haskell or Scala one?
A lambda expression doesn't have a type. It cannot, because any type in the .NET world that it could have, would also hard-code the type of the lambda's parameters and result. Now consider:
x => x + 1
What type could x
have? What type will the result be? There isn't any single answer, and the lambda expression can indeed be converted to Func<int, int>
, Func<double, double>
, and many other delegate types with different parameters. Giving a lambda expression a type would disallow such expressions. C# did want to allow such expressions, so was designed not to give such expressions any type.
This is because () => 5
can be compatible with various delegate types (eg you may have a custom delegate
that takes nothing and returns int
). And in order to create a delegate
, compiler has to know the exact type. It can't just pick a random type that suits your needs. So that's why unless you cast it to an actual delegate type, you can't Invoke
it.
In cases like where a method expects a delegate
, that conversion is implicitly done by the compiler:
void Foo(Func<int> func) { }
Foo(() => 5);
And it is also important to know that delegates
are actually classes behind the scenes. And each time you create a delegate
instance, compiler creates an instance of that class
. So either way you have to specify a type so the compiler will know which type to use.
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