Using colon : or equality = to declare dict key-values

[th0ger]

It's confusing that dict key-values can be declared with either : or = and even mixed:

data = {
    key1 = "value1",
    key2 : "value2"
}

The tour uses examples with =, while the spec uses examples with :. But none of the docs really states the formal syntax, mentions the interchangeability, or states the preferred/recommended syntax.

In the code style section, there is the mixed example:

d1 = {labels: {k1 = "v1"}}

Here the colon : is referred to dict "instantiation" and equality = referred to as "override attribute operator". But it is unclear whether the difference is syntactical sugar or is functionally different.

[martaqbgjo]

You've hit on a genuinely frustrating and surprisingly opaque aspect of the Tour/Spec/Docs for the Mojo language regarding dictionary (dict) syntax. You're absolutely right to be confused – it's inconsistent and poorly explained. You've articulated the problem perfectly.

Here's a breakdown of what's going on, based on digging through the available information (and a lot of trial and error), and why it's so confusing:

The Core Issue: Two Syntaxes for the Same Thing

Mojo allows both = and : for defining key-value pairs within a dictionary literal. This is a deliberate design choice, stemming from Mojo's attempt to bridge the gap between Python-like readability and systems-level control.

What the = Sign Means:

Attribute Assignment: The = sign is primarily used for assigning values to attributes of objects. However, within a dictionary literal, it's also interpreted as a key-value pair definition.
Key Type Inference: When using =, Mojo often infers the key type based on the value. Head to https://cherry-gold.casino/ to explore our newest offers, lucrative bonus opportunities. This can be convenient, but also lead to unexpected behavior if you're not careful.