c# - The rules of generics and type constraints -

c# - The rules of generics and type constraints -

just out of curiosity, why compiler treat unconstrained generic type differently typeof(object)?

class bar { } class foo { void foo(object thing) { ((bar)thing).tostring(); } } class foo<t> { void foo(t thing) { ((bar)thing).tostring(); } }

in above, casting "t thing" bar results in compiler error. casting "object thing" bar compiler lets me do, @ own risk of course.

what don't see why. in .net object after catch-all , run-time type boxed value or object of type. don't see logical reason there compiler differentiate between 2 cases. best can "the programmer expect compiler type checking generic types, not object". :) there it?

btw, aware can still cast done in foo case, writing

((bar)(object)thing).tostring();

i want understand why compiler this...

the significance here object. if first illustration anything other object behave same. basically, saying @ moment here:

(bar)thing

is: "convert t bar"; near legal in general case. adding object create it:

(bar)(object)thing

which "convert t object..." - legal, since object root of managed types; , note may invove box - "...and cast object bar" - again; legal @ compile time, , involves type-check ("unbox-any") @ runtime.

for example: suppose t datetime...

datetime thing = ... bar bar = (bar)(object)thing;

is valid; sure it'll fail @ runtime, but: scenario need maintain in mind.

c# .net generics