[Pitch #2] Build-Time Constant Values

[wowbagger (冀卓疌)]

@stackotter

My main concern with const is not that it would be confused with let, but that reading @const let name = "stackotter" really doesn't tell me very much, assuming that I haven't seen const before. I probably wouldn't associate that with build-time evaluation of expressions and values (especially if I came from a language where it means something else). But if it was @buildTime let name = "stackotter" I think that most people would have a much better first guess at what that means. 'Build-time' isn't necessarily the best phrase for this purpose, but it is certainly less cryptic than const imo.

Also, if build-time mutation of values was added (as some were considering earlier), constant could become a bit of a misnomer.

It wouldn't be the end of the world if @const was chosen, but we're in a position to choose a nice descriptive syntax for this new feature, and the more intuitive the syntax is, the easier and faster it is to learn.

I want to add to this by by borrowing some other words of mine from the last pitch:

@wowbagger

As many upthread have pointed out, "constant", which "const" is short for, is too close in meaning in English to "immutable". This in my opinion makes the feature less teachable if we use the const spelling, because both "constant" and "immutable" have been used in documentation to describe let properties/values/declarations.

A search for "constant" in the latest TSPL shows 340 result:

I did not check each of the 340 results, but all those that I checked use "constant" for let . Meanwhile, "immutable" only shows up 3 times:

This shows a clear history of "constant" being used as the primary description for let . It will be difficult for people new to the language to learn that even though we call let "constants", we only write const for some of them in code, and they are treated differently from other "constants", because they're const . Even for people already familiar with the language, const in my opinion still messes with the mental model after they have learnt about it. Because although writing in Swift is not writing in English, your understanding of the English word still seeps in when you use the word.