WIP: Add only function
#3
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The function `only(x)` returns the one-and-only element of a collection `x`, or else throws an error.
| only(x::NamedTuple{<:Any, <:Tuple{Any}}) = first(x) | ||
| only(x::NamedTuple) = throw( | ||
| ArgumentError("NamedTuple contains $(length(x)) elements, must contain exactly 1 element") | ||
| ) |
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Not sure of style in Base, but this fits with other files as far as I can tell...
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I am tempted to say this should be a BoundsError or a DimensionMismatch ?
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- yeah, I can see the case for
BoundsErroras the error type... but on the other hand the message doesn't really feel right
julia> x = [1, 2];
julia> throw(BoundsError(x, 2))
ERROR: BoundsError: attempt to access 2-element Array{Int64,1} at index [2]-
Similarly, with
DimensionMismatch, what is the "mismatch"? -
ArgumentErrorfeels better to me... but i'd certainly like to hear other opinions!
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You made a PR tio invenia/julia. |
| only(x::Tuple) = throw( | ||
| ArgumentError("Tuple contains $(length(x)) elements, must contain exactly 1 element") | ||
| ) | ||
| only(a::AbstractArray{<:Any, 0}) = @inbounds return a[] |
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Is it not possible to construct a zero length AbstractArray{<:Any, 0} ?
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How do I test that? i.e. How does one create a zero-dim array of any length?
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julia> collect(1)
0-dimensional Array{Int64,0}:
1
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Idk how to create an empty one
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I do not know the answer to this (and Andy Ferris is the wise fellow who actually wrote this)
I will take that as a word of encouragement! |
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Thanks for reviewing -- moved to JuliaLang#33129 |
Previously, we might accidentally leave behind content in the fields
that should not be there. For example:
```
julia> code_typed(() -> (TypeVar(:x),), (), optimize=false)
1-element Vector{Any}:
CodeInfo(
@ REPL[1]:1 within `#3'
1 ─ %1 = Main.TypeVar(:x)::Core.Compiler.PartialTypeVar(x, true, true)
│ %2 = Core.tuple(%1)::Core.PartialStruct(Tuple{TypeVar}, Any[Core.Compiler.PartialTypeVar(x, true, true)])
└── return %2
) => Tuple{TypeVar}
julia> ans[1][1].rettype
Core.PartialStruct(Tuple{TypeVar}, Any[Core.Compiler.PartialTypeVar(x, true, true)])
```
The function
only(x)returns the one-and-only element of a collectionx, or else throws an error.