[ruby-core:115675] [Ruby master Feature#20054] Replace the use of `def` in endless method definitions with a new sigil

Issue #20054 has been updated by rubyFeedback (robert heiler).


I should also say that I understand sawa's argument too; the

    def foo = method_body

really does look a bit weird without "end". My eyes (or rather my
brain) have adapted to assuming a nice "end" being part of a method.
It does not affect me personally, though, as I don't use that
syntax variant. I stick with oldschool "def foo; end".

----------------------------------------
Feature #20054: Replace the use of `def` in endless method definitions with a new sigil
https://bugs.ruby-lang.org/issues/20054#change-105609

* Author: sawa (Tsuyoshi Sawada)
* Status: Open
* Priority: Normal
----------------------------------------
I propose to remove the use of keyword `def` from the syntax of endless method definition, and introduce a new sigil instead of it. There are several possibilities for what character to use as the sigil, but the most seemingly promising one to me at this point is the colon. So, instead of:

```rb
def foo = method_body
```

I propose to write

```rb
:foo = method_body
```

There a few reasons to dispense with `def` in endless method definition.

First, the current syntax for endless method definition looks too similar to conventional method definition. Without endless method definition, we could already define a method in a single line:

```rb
def foo; method_body end
```

and compared to this, what the endless method definition does is that, it only saves you from typing the `end` keyword just by replacing the semicolon with an equal sign. This actually had not made much sense to me. Just saving you from typing the keyword `end` looks too small of a change for introducing new syntax. In order for endless method definition syntax to be justified (as a shorthand for conventional method definition), it needs to save more typing.

Second, in #19392, some people are claiming to change the precedence involving endless method definition. I agree with Matz and other developers who support the current precedence in which:

```rb
def foo = bar and baz
```

is interpreted as:

```rb
(def foo = bar) and baz
```

and I understand that the controversy is due to the look and feel of the keyword `def`. `def` has lower precedence than `and` in conventional method definition, although `=` has higher precedence than `and` in variable/constant assignment. Mixing the low-precedence `def` and the high-precedence `=` into a single syntax was the cause of the trouble, according to my opinion.

Thence, we should get rid of `def`. Once we do so, we need to distinguish endless method definition from variable/constant assignment in a new way. What came to my mind was to use a single character: a sigil.

Especially, using the colon seems to make sense to me for several reasons:

Most importantly, assignment to a symbol is impossible, and it currently raises a syntax error, so it would not conflict with variable/constant assignment syntax.

Within Ruby syntax, symbol is naturally used to represent a method name. For example, in `foo(&:bar)` constructions, users are used to passing a method name as a symbol. Also, a method definition returns a symbol representing the method name. So, making the endless method definition syntax look superficially like an "assignment to a symbol" would make sense.



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