Working with strings/path is awkward

[sagikazarmark]

Given let filename: String! = "file.ext", filename.split(".")[0] returns String, not String! which is understandable.

But I can't find a good way to construct a path from this:

let dirname = filename.split(".")[0]

Failing cases

let name: String! = "/work/" + dirname

# Doesn't turn dirname into String!
assert { dirname != null }

let name: String! = "/work/" + dirname

The best solution I found so far:

# Make sure it's actually non-nil
assert { dirname != null }

let name = ["/work", filename.split(".")[0]].join("/")

I might be missing something, but I couldn't find a better solution so far.

[vito]

Dang implements flow typing for nullability checks, so you can do this:

let dirname = filename.split(".")[0]
let name = if (dirname != null) {
  "/work/" + dirname
} else {
  "/work"
}

It was kind of brittle in the past but I just merged some improvements in #60 - meaning you can now do this:

if (dirname == null) {
  return # or raise
}

# in this path, dirname is now String!

And it also handles if (foo != null and bar != null) whereas before it didn't work with and or or.

There's also ?? if you want to resolve nulls inline, like "/work/" + (dirname ?? "").

I haven't added assert support - it's a good thought, but tragically I just recently converted it from a built-in language feature to a stdlib function, so that option just went away. 😅

[sagikazarmark]

In this particular scenario (filename.split(".")[0]), I know there is always a value at the zero index, so I'd like to coerce null to string.

Or better yet, throw an error if it's null.

For example:

let dirname = filename.split(".")[0]?

If null, raise an error
If not null, return the value.

[vito]

@sagikazarmark Ah gotcha. I've been tempted to add a ! postfix operator for exactly that. I think ! makes more sense since it's casting/asserting non-null and adding ! to the type. Compared to ? from JS/TS which goes in the other direction - preserves null without calling the chain, which is actually what Dang does by default (mirroring GraphQL):

❯ node
> [new Date()][1].toString()
Uncaught TypeError: Cannot read properties of undefined (reading 'toString')
> [new Date()][1]?.toString()
undefined

❯ dang
dang> [container][2].id
=> null

[sagikazarmark]

Works for me