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recommend explicit using Foo: Foo, ... in package code (was: "using considered harmful") #42080

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9 changes: 9 additions & 0 deletions base/docs/basedocs.jl
Original file line number Diff line number Diff line change
Expand Up @@ -37,6 +37,15 @@ kw"help", kw"Julia", kw"julia", kw""
available for direct use. Names can also be used via dot syntax (e.g. `Foo.foo` to access
the name `foo`), whether they are `export`ed or not.
See the [manual section about modules](@ref modules) for details.

!!! note
Qualifying the names being used as in `using Foo: Foo, f` is
recommended over plain `using Foo` for released packages and other
code which is meant to be re-used in the future with updated dependencies
or future versions of julia. When two modules or packages export the same name
and both are loaded with `using` (without the explicit list), it is an error to use
that name without qualification. Using an explicit list ensures that new exports
in updated dependencies do not break the forward compatibility of the code.
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"""
kw"using"

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13 changes: 12 additions & 1 deletion doc/src/manual/modules.md
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Expand Up @@ -112,7 +112,7 @@ and above. To maintain compatibility with Julia 1.10 and below, use the `@compat

### Standalone `using` and `import`

Possibly the most common way of loading a module is `using ModuleName`. This [loads](@ref
For interactive use, the most common way of loading a module is `using ModuleName`. This [loads](@ref
code-loading) the code associated with `ModuleName`, and brings

1. the module name
Expand Down Expand Up @@ -168,6 +168,17 @@ Importantly, the module name `NiceStuff` will *not* be in the namespace. If you
julia> using .NiceStuff: nice, DOG, NiceStuff
```

!!! note
Qualifying the names being used as in `using Foo: Foo, f` is
recommended over plain `using Foo` for released packages, and other
code which is meant to be re-used in the future with updated dependencies
or future versions of julia.

The reason for this is if another dependency starts to export one of the
same names as `Foo` and you attempt to use that name, then previously working
code will error due to an ambiguity in which package the name should be
taken from.
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Julia has two forms for seemingly the same thing because only `import ModuleName: f` allows adding methods to `f`
*without a module path*.
That is to say, the following example will give an error:
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