catch2 compile error with non-ostreamable types due to range io

[timblechmann]

catch2 has some range matchers like RangeEquals. however i'm running into the following problem:

• my underlying type is not ostreamable
• view_interface provides operator<< unless IO is explicitly disabled via RANGES_V3_DISABLE_IO
• catch2's range matchers will try to stringify the range via operator<<

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as a workaround i can compile my unit tests with RANGES_V3_DISABLE_IO, but i wonder if view_interface::operator<< can be enabled only if the underlying type supports operator<<?