Virtual method calls are simple: you just look up the method slot in a vtable and call the function pointer. Easy! Well, not quite: interfaces present a kind of multiple inheritance, and things quickly become complicated.

This post discusses interface method calls in C++ (GCC), Java (OpenJDK/HotSpot), C# (CLR), Go, and Rust.

It is an expanded version of my answer on Software Engineering Stack Exchange on Implementation of pure abstract classes and interfaces.

This article explains the difference between dynamic dispatch (late binding) and static dispatch (early binding). We’ll also touch on the differences in language support for virtual and static methods, and how virtual methods can be circumvented.

Global dependencies make it difficult to properly test a piece of code. By extracting all dependencies into a single manageable object, we can easily mock the necessary services and avoid a large-scale refactor.