[API Proposal]: DI container should respect generic constraints when resolving single instance. #108874
Description
Background and motivation
I expected that this merge would support resolving not only collections of constructed generic types but also a single instance.
While C class can be resolved without any issue, I get exception when resolving an instance of class D:
void Main()
{
var sc = new ServiceCollection();
sc.AddSingleton(typeof(IFoo<>), typeof(Foo1<>));
sc.AddSingleton(typeof(IFoo<>), typeof(Foo2<>));
sc.AddSingleton<C>();
sc.AddSingleton<D>();
var sp = sc.BuildServiceProvider();
var c = sp.GetRequiredService<C>();
var d = sp.GetRequiredService<D>();
}
public class C
{
public IFoo<Bar>[] Foos {get;}
public C(IEnumerable<IFoo<Bar>> foos)
{
Foos = foos.ToArray();
}
}
public class D
{
public IFoo<Bar> Foo { get; }
public D(IFoo<Bar> foo)
{
Foo = foo;
}
}
public class Bar
{
public Bar(int i)
{
}
}
public interface IFoo<T>
{
void Throw();
}
public sealed class Foo1<T> : IFoo<T>
{
public void Throw()
{
throw new NotImplementedException();
}
}
public sealed class Foo2<T> : IFoo<T>
where T : IEquatable<T>
{
public void Throw()
{
throw new InvalidOperationException();
}
}
API Proposal
My expectation is that for a single instance the semantics should be equivalent to injecting a collection of valid instances and then taking the last one. But apparently this is not how container works currently.
API Usage
Nothing should change for api, only behavior.
Alternative Designs
No response
Risks
No response