c# - Understanding Func<T, TResult> Delegate with MVC -

i trying wrap head around func < t, tresult> delegate seems not clear. know t parameter & tresult return type.

in mvc use function time:

@model products @html.textboxfor(s=>s.my_property) 

now how textboxfor function knows parameter passed me "products model".

and below signature textboxfor model:

public static mvchtmlstring textboxfor<tmodel, tproperty>(     htmlhelper<tmodel> htmlhelper,     expression<func<tmodel, tproperty>> expression,     idictionary<string, object> htmlattributes ) 

so question is, when call html.textboxfor(s), how come method knows "s" "products" model , how tmodel maps parameter "s" (knowing product model , need return something)?

the html property (@html) of type htmlhelper<products>, because of @model products directive. how razor engine works.

textboxfor extension method htmlhelper<tmodel>, , in code, you're calling on instance of htmlhelper<products>, therefore tmodel resolved products.

then, compiler can bind tproperty type of my_property there, knows tmodel , can deduce lambda "returns".

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side note: must know expression<func<t>> totally different func<t>:

• func<...> simple delegate, reference piece of executable code somewhere, opaque.
• expression<func<...>>, on other hand, expression tree, kind of ast.

when write lambda, compiler generates different code depending on whether you're assigning lambda func<...> or expression<func<...>>. in first case, compile lambda , generate delegate. in second case, emit expression tree.

for in-depth explanation, can read eric lippert's series lambda expressions vs. anonymous methods: part 1, part 2, part 3, part 4, part 5