> or those are a primitive type and you're just calling a function builtin the language itself
You’re thinking at a different level of abstraction to the Zig developers. Summing a primitive type is going to be turned into a couple of machine opcodes (but no branch instruction) and will usually be constant time, whereas an explicit function call will require pushing pc to the stack and jumping elsewhere, executing any number of instructions once there, taking an arbitrarily long time, making it more difficult to reason about.
You’re thinking at a different level of abstraction to the Zig developers. Summing a primitive type is going to be turned into a couple of machine opcodes (but no branch instruction) and will usually be constant time, whereas an explicit function call will require pushing pc to the stack and jumping elsewhere, executing any number of instructions once there, taking an arbitrarily long time, making it more difficult to reason about.