[mikulas_florek]

It's hard to discuss this without using any specific "type-safe" language.

1. you can have the same problem in type-safe language, since it will probably have cast to int too 2. do not use builtin operators in C for that, instead create new functions, e.g. addMeters(Meters a, Meters b); 3. hide the int in *.c file

[jasode]

Look at the common theme among your suggestions:

  - do not use builtin operators in C for that, 
  - instead create new functions, e.g. addMeters()
  - hide the int in *.c file

Those are "best practices" instead of compiler-enforced type-check errors. Likewise, suggesting a best practice such as "don't free() memory twice" is not the same as a GC-language (Lisp/Java/C#/Go) freeing memory on the programmer's behalf or a static-ownership checker (Rust) preventing a programmer from making that mistake.

[kazinator]

Don't free memory two or more times is "OMG don't flippin' do that", not a "best practice". ;)

"Best practice" is a choice from among justifiable alternatives.

[mikulas_florek]

You can write the exact same wrong code in e.g. C#

  public class Meters { public int x; }
  public class Yards { public int x; }
  public class Kilograms { public int x; }

  Meters m = ...
  Yards y = ...
  Kilograms k = ...
  k.x = m.x + y.x;

all my sugestions for C are basically the same in C#

  - do not use builtin operators in C# for that instead create new functions, e.g. addMeters()
  - hide the int in *.c file == make it private in c#

[fiedzia]

> you can have the same problem in type-safe language

Yes, you can. But at least you have a better option and better chance of other people using it, so statistically you'll have less errors.

> do not use builtin operators in C for that

No, do not add another rule to a million of rules people have to already follow, make compiler worry about enforcing that, not developer.

[mikulas_florek]

> Yes, you can. But at least you have a better option and better chance of other people using it, so statistically you'll have less errors.

I highly doubt that this specific bug would not happen in any typesafe language. The only way I see this not happening is if there is no native float-like type. Is there such language? They could have make it safe in C, and they did not, probably because it's convenient to use float.

> No, do not add another rule to a million of rules people have to already follow, make compiler worry about enforcing that, not developer.

It can be implemented in C so it's forced by compiler.