BUG: Drop explicit <double> template arg from std::abs in test#600
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On macOS SDK 26.5's <__math/abs.h>, the std::abs overload set includes
both the templated floating-point form and integer-typed candidates,
making the explicit form `std::abs<double>(...)` ambiguous:
error: call to 'abs' is ambiguous
37 | return std::abs<double>(input - desired)
| ^~~~~~~~~~~~~~~~
The explicit template argument was never load-bearing here --- inputs
are `double`, so the non-templated `std::abs(double)` overload from
<cmath> resolves unambiguously. Dropping `<double>` fixes the build
on current Apple toolchains without changing behavior on earlier
SDKs or other platforms.
Surfaced while validating BRAINSia#598 (find_package(ANTS)
migration) on AppleClang 21 / macOS SDK 26.5.
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Drop the explicit
<double>template argument fromstd::absinitkResampleInPlaceImageFilterTest.cxx, which became ambiguous on macOS SDK 26.5 / AppleClang 21 and broke the test build.Root cause
macOS SDK 26.5's libc++ exposes the
std::absoverload set via<__math/abs.h>, where theint/long/long longoverloads plus the floating-point template are all visible. Writingstd::abs<double>(...)forces template-argument deduction and leaves the integer candidates viable, so overload resolution is ambiguous:The explicit template argument was never load-bearing: the inputs are
double, so the non-templatestd::abs(double)from<cmath>is an exact match and resolves unambiguously. Dropping<double>fixes the build on current Apple toolchains with no behavior change on earlier SDKs or other platforms.Surfaced while validating #598 (find_package(ANTS) migration) on AppleClang 21 / macOS SDK 26.5.
Local validation
Verified on the exact toolchain that surfaced the bug (Apple clang 21.0.0, arm64-apple-darwin25.5.0), compiling via
ccache clang++ -std=c++17:std::abs<double>(...)→error: call to 'abs' is ambiguous(candidates from MacOSX.sdk<__math/abs.h>).std::abs(...)→ compiles cleanly (exit 0).pre-commit run --all-filespasses.