add "use = not : for initialization and named parameters" draft

_languages/use-equals-not-colon-for-initialization-and-named-parameters.md

@@ -0,0 +1,99 @@
+---
+title:  "Language Design: Use `=`, not `:` for Initialization and Named Parameters (WIP)"
+date:   2023-09-20
+---
+
+# DRAFT
+
+## The Problem, explained using Rust as a cautionary tale
+
+Rust has two distinct syntactic variants for "invocations"[^1] ...
+- one for calling functions and
+- one for initializing structs and enums[^2]
+
+... that provide different affordances and features:
+
+- struct initializer arguments can be named, and can also use a shorthand notation
+- method arguments cannot be named, and what looks like shorthand notation is just positional arguments
+
+The following example shows both:
+
+```rust
+struct User {
+  active: bool,
+  username: String,
+  email: String,
+  sign_in_count: u64,
+}
+
+fn user(email: String, username: String) -> User {
+  User {
+    active: true,
+    username,
+    email,
+    sign_in_count: 0,
+  }
+}
+
+fn main() {
+  user("jane@example.com".into(), "Jane Example".into());
+}
+```
+
+### Diverging Code Styles and Best Practices
+
+In practice this means that you have diverging recommendations and best practices (option structs, default hacks, builders etc.)
+for dealing with issues like "this thing has grown and is taking way too many parameters now".
+
+And every improvement that is going to be made will change the scale slightly, causing churn due to another thing becoming the next "best practice".
+(And most likely only apply to either struct/enum init *or* method calls, but not both.)
+
+
+### Needless Ambiguity
+
+Structs using `{` also means that something as trivial as `if foo {` is ambiguous in Rust.
+
+
+### Lack of Consistent Rules for Type Ascriptions
+
+It breaks the consistency of always being able to rely on while reading that `: Foo` is a type ascription.
+Languages from the 70ies managed to get this right, Rust somehow regressed on that, failing to ship
+[type ascriptions](https://rust-lang.github.io/rfcs/0803-type-ascription.html) and
+[giving up on it after 8 years](https://rust-lang.github.io/rfcs/3307-de-rfc-type-ascription.html).
+
+
+### Default Parameters Made Hard
+
+Using `:` for struct initialization means that it's not a good syntax options for extending the language for default parameters:
+
+    struct X { x: String: "foo" } // ugly
+
+## The Solution
+
+What should they have done:
+
+- Function calls, method calls, struct init, enum init consistently use `()`, not a random mix of `{}` and `()`
+- Have *one* ruleset that all those invocation follow.
+- Use `=` for named parameters, such that everything works if default parameters are added in the future.
+- Shorthand notation or positional arguments? Pick one.
+
+#### How to Distinguish between a variable assigment and a named parameter use inside a function invocation?
+
+Example:
+
+    fun someFunction(a: Int64) = ...
+    var a = 12;
+    let b = 23
+    someFunction(a = b) // what does this mean?
+
+Single rule: inside a functions argument list, the first level of `=` use is always a named parameter and never a
+variable assignment, even if some variable `a` would be in scope.[^3]
+
+If a variable assigment inside a function argument list is still needed, it could be expressed as: 
+
+    someFunction(a = { a = b; b }) // still possible
+
+
+[^1]: Using the term "invocations" loosely here. It's almost guaranteed that Rust fans show up anyway going "ackchyually" while completely missing the point, but hey – I tried.
+[^2]: Except the tupled version of enums, for which initializers look like function calls again.
+[^3]: Also, variable assignment returns `Unit`, so we never have to decide, right? RIGHT?