[unwind]

I was not familiar with the term, so I had to look it up. It's about code like this:

    a := b

the `:=` looks vaguely like a walrus. The most common reference language seems to be Python [1]. The usage is for making assignment remain an expression, so you can do stuff like

    area = (width := get_width()) * (height := get_height())

or something, and have the top-level expression remain valid since the sub-expressions are assignments that remain expressions, i.e. the assigned value is also the result of the expression.

[1]: https://realpython.com/python-walrus-operator/

[jessekv]

Its also one of the more controversial features and its introduction sparked Guido's stepping down.

Since it was introduced, I have been looking but there has been only a handful of times where I could use it to write clearer code.

I'm curious if anyone actually likes it.

edit: A quick search shows that I do use it regularly in while loops, e.g.:

  while result := my_fun():
    ...

[rich_sasha]

IIRC he stepped down because he thought it's a good feature and people pointlessly moaned about it. Not because he thought it's controversial and has enough.

I used it a small handful of times. But it also seems like quite a source of footguns. Many examples here: https://github.com/satwikkansal/wtfpython rely on the misuse of the walrus operator.

[miohtama]

I have written Python since 2003 and used walrus only once. It's unnecessary.

[singhrac]

Eh, I write a lot of Python and while it's unnecessary, it can make code easier to read if not overused.

  if (config_fn := base_dir / "config").exists():
      ...

is just a tiny bit shorter than this:

  config_fn = base_dir / "config"
  if config_fn.exists():
      ...

but if you do this enough times (if you are handling a lot of possible errors / missing data, etc.) it can definitely shorten the code.

[jessekv]

If you have to wrap it in parens, it might be shorter but it's not really clearer.

In other contexts, parens are a good indication it's time for a new line.

But I can agree something like this does look clean and clear:

  if value := obj.get("key"):
      ...

[zem]

python's use is the unusual one; the most common use (dating all the way back to algol) is to use it for assignment, so you can use = for equality.

https://en.wikipedia.org/wiki/Assignment_(computer_science)#...

[rob74]

Go uses "==" for equality checks, "=" for assignments, and ":=" for "declaration/assignment with type inference" - so it's different from both Python (you can use ":=" as part of an expression in Go too, but you can also use "=") and Algol/Pascal (where it's used only for assignment).

[weinzierl]

In math = is used for equality and := for definition[1] which is probably the closest thing to assignment in a programming language. That is why Pascal and similar languages use = for equality only and := for assignment.

That always made more sense to me than = for assignment and more =s for different kinds of equality, but in the end this syntax discussions are always just bike-shedding.