[db48x]

Absolutely. This is an example of the poor design of the C language. Other languages that were around at the time C was created choose `:=` as assignment and `=` for equality tests, making this type of typo quite impossible.

Common Lisp makes the Hamming distance even larger; equality tests are written as `(eq foo bar)`, while changing a value is `(setf foo bar)`. Common Lisp may have features which are undesirable in an OS kernel (garbage collection), but it does make the code wonderfully clear and easy to read.

[ed25519FUUU]

:= Still seems easy to overlook at a cursory glance.

[kazinator]

What db48x neglected to mention is that some of those languages also featured assignment as strictly a statement; it could not be a subexpression. As in:

   fun(x := 42);   (* syntax error in Pascal *)

   x := 42;  (* OK *)

   x = 42; (* hopefully a statement with no effect warning *)

If assignment is a statement, it's possible to use the same token. Classic BASIC:

   10 X = 5
   20 IF X = 5 GOTO 10

This doesn't cause the C problem of mistaken assignment in place of a test, so it's rather ironic that C managed to shoot itself in the foot in spite of dedicating twice the number of tokens.

[a1369209993]

That is true, but has nothing to do with "==" vs "=" vs ":=". You can do:

  func(x = 42); /* syntax error: expression operator expected, got '=' */
  x = 42; /* OK */
  x == 42; /* warning: statement expression has no effect */

just fine if you require "=" to be a statement.

[db48x]

I'd forgotten that!