entity framework - Why can't I create a callback for the List Find method in Moq? -

i created extension method lets me treat list dbset testing purposes (actually, found idea in question here on stack overflow, , it's been useful). coded follows:

    public static dbset<t> asdbset<t>(this list<t> sourcelist) t : class     {         var queryable = sourcelist.asqueryable();          var mockdbset = new mock<dbset<t>>();         mockdbset.as<iqueryable<t>>().setup(m => m.provider).returns(queryable.provider);         mockdbset.as<iqueryable<t>>().setup(m => m.expression).returns(queryable.expression);         mockdbset.as<iqueryable<t>>().setup(m => m.elementtype).returns(queryable.elementtype);         mockdbset.as<iqueryable<t>>().setup(m => m.getenumerator()).returns(queryable.getenumerator());         mockdbset.setup(d => d.add(it.isany<t>())).callback<t>(sourcelist.add);         mockdbset.setup(d => d.find(it.isany<object[]>())).callback(sourcelist.find);         return mockdbset.object;     } 

i had been using add awhile, , works perfectly. however, when try add callback find, compiler error saying can't convert method group action. why sourcelist.add action, sourcelist.find method group?

i'll admit i'm not particularly familiar c# delegates, it's i'm missing obvious. in advance.

the reason add works because list<t>.add method group contains single method takes single argument of type t , returns void. method has same signature action<t> 1 of overloads of callback method (the 1 single generic type parameter, callback<t>), therefore list<t>.add method group can converted action<t>.

with find, trying call callback method (as opposed callback<t>) expects action parameter (as opposed action<t>). difference here action not take parameters, action<t> takes single parameter of type t. list<t>.find method group cannot converted action because find methods (there 1 anyway) take input parameters.

the following compile:

    public static dbset<t> asdbset<t>(this list<t> sourcelist) t : class     {         var mockdbset = new mock<dbset<t>>();         mockdbset.setup(d => d.find(it.isany<object[]>())).callback<predicate<t>>(t => sourcelist.find(t));         return mockdbset.object;     } 

note have called .callback<predicate<t>> because list<t>.find method expects , argument of type predicate. note have had write t => sourcelist.find(t) instead of sourcelist.find because find returns value (which means doesn't match signature of action<predicate<t>>). writing lambda expression return value thrown away.

note although compiles not work because dbset.find method takes object[] it's parameter, not predicate<t>, have this:

    public static dbset<t> asdbset<t>(this list<t> sourcelist) t : class     {         var mockdbset = new mock<dbset<t>>();         mockdbset.setup(d => d.find(it.isany<object[]>())).callback<object[]>(keyvalues => sourcelist.find(keyvalues.contains));         return mockdbset.object;     } 

this last point has more how use moq library how use method groups, delegates , lambdas - there sorts of syntactic sugar going on line hiding relevant compiler , isn't.