Conditional continuation operator for options #9161
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This is usually called "existential operator". I think it's better if you use this name in the docs. Searching for "continuation operator" in Google brings results for "line continuation" |
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Aah, good idea. Wasn't really sure what to call this |
| injected = nnkDotExpr.newTree( | ||
| nnkDotExpr.newTree(opt, newIdentNode("unsafeGet")), firstBarren) | ||
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| result = quote do: |
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That it's wrapped in a proc? Any idea how to avoid it?
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this pattern (https://en.wikipedia.org/wiki/Immediately-invoked_function_expression) in Nim can use block expressions:
var i = 0
let a = block:
if i == 0:
i+2
else:
i*3
echo a
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The logic in the current procedure is not that simple though, this is what would be generated for something that returns a value:
(proc (): auto =
let :tmp130615 = x
if :tmp130615.isSome:
return some(:tmp130615.unsafeGet.slice(3)[0]))()As you can see it uses auto as the type and relies on Nim to create the default none value regardless of the type, so it doesn't have an else branch to the if case. I tried wrapping this up in a block statement, but without luck.
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| result = quote do: | |
| result = quote do: | |
| (proc (): auto {.inline.} = |
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Yeah making it inline is probably a good idea, but if I apply your suggested cange it would be a double proc wouldn't it? Not sure how this new, fancy, GitHub feature works :P
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oh i see, guess I used that new feature wrong myself; maybe just apply the change manually then
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| ## will be ``Option[T]`` where ``T`` is the returned type of ``statements``. | ||
| ## If nothing is returned from ``statements`` this returns nothing. | ||
| ## | ||
| ## .. code-block:: nim |
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runnableExamples + doAssert's instead of echo's ? (otherwise nothing guarantees it stays in sync or keeps compiling)
It doesn't, |
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Well it rewrites it to something that should work with the original order: (proc (): auto =
let x = a # In case `a` is a procedure that returns an option
if x.isSome: # Note that this has no else branch, relies on `auto` and the default value of `option` to resolve this
some(x.unsafeGet.b[c])
)()Shouldn't that keep the ordering the same? |
| return some(`injected`) | ||
| )() | ||
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| when isMainModule: |
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Now we have optionsutils package which implements all the features proposed in this PR. Closing. |
This adds a Rust-like
?.operator to Nim which will only evaluate further if the value of the preceding option is a some. In that case it will unwrap the value and pass it on to the right hand side. The entire thing returns an option of the final value, or none if the left hand side is a none, or nothing in case the right hand side doesn't return anything.Depends on PR #9160