Matt Godbolt sold me on Rust by showing me C++

Yes, Rust is better. Implicit numeric conversion is terrible. However, don't use atoi if you're writing C++ :-). The STL has conversion functions that will throw, so separate problem.

> Implicit numeric conversion is terrible.

It's bad if it alters values (e.g. rounding). Promotion from one number representation to another (as long as it preserves values) isn't bad. This is trickier than it might seem, but Virgil has a good take on this (https://github.com/titzer/virgil/blob/master/doc/tutorial/Nu...). Essentially, it only implicitly promotes values in ways that don't lose numeric information and thus are always reversible.

In the example, Virgil won't let you pass "1000.00" to an integer argument, but will let you pass "100" to the double argument.

Aside from the obvious bit size changes (e.g. i8 -> i16 -> i32 -> i64, or f32 -> f64), there is no "hierarchy" of types. Not all ints are representable as floats. u64 can represent up to 2^64 - 1, but f64 can only represent up to 2^53 with integer-level precision. This issue may be subtle, but Rust is all about preventing subtle footguns, so it does not let you automatically "promote" integers to float - you must be explicit (though usually all you need is an `as f64` to convert).

> Aside from the obvious bit size changes (e.g. i8 -> i16 -> i32 -> i64, or f32 -> f64), there is no "hierarchy" of types.

Depends on what you want from such a hierarchy, of course, but there is for example an injection i32 -> f64 (and if you consider the i32 operations to be undefined on overflow, then it’s also a homomorphism wrt addition and multiplication). For a more general view, various Schemes’ takes on the “numeric tower” are informative.