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restore fallback 3-arg setprecision method (#58586) #58699

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Merged
merged 1 commit into from
Jun 12, 2025
Merged

restore fallback 3-arg setprecision method (#58586) #58699

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5 changes: 5 additions & 0 deletions NEWS.md
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Original file line number Diff line number Diff line change
Expand Up @@ -134,6 +134,8 @@ New library features
* `Timer` now has readable `timeout` and `interval` properties, and a more descriptive `show` method ([#57081]).
* `sort` now supports `NTuple`s ([#54494]).
* `map!(f, A)` now stores the results in `A`, like `map!(f, A, A)` or `A .= f.(A)` ([#40632]).
* `setprecision` with a function argument (typically a `do` block) is now thread safe. Other forms
should be avoided, and types should switch to an implementation using `ScopedValue` ([#51362]).

Standard library changes
------------------------
Expand Down Expand Up @@ -225,8 +227,10 @@ Tooling Improvements
[#40989]: https://github.com/JuliaLang/julia/issues/40989
[#45793]: https://github.com/JuliaLang/julia/issues/45793
[#49355]: https://github.com/JuliaLang/julia/issues/49355
[#49933]: https://github.com/JuliaLang/julia/issues/49933
[#50988]: https://github.com/JuliaLang/julia/issues/50988
[#51149]: https://github.com/JuliaLang/julia/issues/51149
[#51362]: https://github.com/JuliaLang/julia/issues/51362
[#51810]: https://github.com/JuliaLang/julia/issues/51810
[#52103]: https://github.com/JuliaLang/julia/issues/52103
[#52999]: https://github.com/JuliaLang/julia/issues/52999
Expand Down Expand Up @@ -284,3 +288,4 @@ Tooling Improvements
[#57087]: https://github.com/JuliaLang/julia/issues/57087
[#57109]: https://github.com/JuliaLang/julia/issues/57109
[#57253]: https://github.com/JuliaLang/julia/issues/57253
[#57727]: https://github.com/JuliaLang/julia/issues/57727
20 changes: 20 additions & 0 deletions base/mpfr.jl
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Expand Up @@ -1178,9 +1178,29 @@ Often used as `setprecision(T, precision) do ... end`
Note: `nextfloat()`, `prevfloat()` do not use the precision mentioned by
`setprecision`.

!!! warning
There is a fallback implementation of this method that calls `precision`
and `setprecision`, but it should no longer be relied on. Instead, you
should define the 3-argument form directly in a way that uses `ScopedValue`,
or recommend that callers use `ScopedValue` and `@with` themselves.

!!! compat "Julia 1.8"
The `base` keyword requires at least Julia 1.8.
"""
function setprecision(f::Function, ::Type{T}, prec::Integer; kws...) where T
depwarn("""
The fallback `setprecision(::Function, ...)` method is deprecated. Packages overloading this method should
implement their own specialization using `ScopedValue` instead.
""", :setprecision)
old_prec = precision(T)
setprecision(T, prec; kws...)
try
return f()
finally
setprecision(T, old_prec)
end
end

function setprecision(f::Function, ::Type{BigFloat}, prec::Integer; base::Integer=2)
Base.ScopedValues.@with(CURRENT_PRECISION => _convert_precision_from_base(prec, base), f())
end
Expand Down