> like the compiler is taking type information and using it to make implicit casts throughout the program. It's not a cast. Rather, it's an inferred/omitted ty

> like the compiler is taking type information and using it to make implicit casts throughout the program. It's not a cast. Rather, it's an inferred/omitted type parameter. In this case, the collect() method is actually collect::<ContainerType>(). So it's not that collect returns something to be cast, but rather that there is a different collect() implementation for each target type. When the compiler is able to infer the target type unambiguously -- for example here, because you assign it to a typed variable -- then you don't have to specify it.