Permit arithmetic operations with more types #229
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The goal of these `std::is_arithmetic` SFINAE uses was to avoid ambiguous overloads when we multiply a `Quantity` with another `Quantity`. It was only ever a shortcut. It seems to work well in most cases, but recently, a user pointed out that it doesn't help `std::complex`. (To be clear, we could _form_ a `Quantity` with `std::complex` rep, but we couldn't multiply or divide a `Quantity` with a `std::complex` scalar.) This PR takes a different approach. First, we define what constitutes a valid "rep". We're very permissive here, using a "deny-list" approach that filters out empty types, known Au types, and other libraries' units types (which we detect via our `CorrespondingQuantity` trait). Incidentally, this should give us a nice head start on #52. Next, we permit an operation (multiplication or division) depending on how the "candidate scalar" type would interact with the Quantity's rep: simply put, the result must itself both exist, and be a valid rep. The net result should be that we automatically consider a much wider variety of types --- including complex number types from outside the standard library --- to be valid scalars. Crucially, this should also be able to avoid breaking existing code: we are introducing potentially a _lot_ of new overloads for these operators, and we can't allow any to create an ambiguity with existing overloads.
chiphogg
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release notes: 🐛 lib (bugfix)
geoffviola
approved these changes
Apr 25, 2024
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The goal of these
std::is_arithmeticSFINAE uses was to avoidambiguous overloads when we multiply a
Quantitywith anotherQuantity. It was only ever a shortcut. It seems to work well in mostcases, but recently, a user pointed out that it doesn't help
std::complex. (To be clear, we could form aQuantitywithstd::complexrep, but we couldn't multiply or divide aQuantitywitha
std::complexscalar.)This PR takes a different approach.
First, we define what constitutes a valid "rep". We're very permissive
here, using a "deny-list" approach that filters out empty types, known
Au types, and other libraries' units types (which we detect via our
CorrespondingQuantitytrait). Incidentally, this should give us anice head start on #52.
Next, we permit an operation (multiplication or division) depending on
how the "candidate scalar" type would interact with the Quantity's rep:
simply put, the result must itself both exist, and be a valid rep.
The net result should be that we automatically consider a much wider
variety of types --- including complex number types from outside the
standard library --- to be valid scalars. Crucially, this should also
be able to avoid breaking existing code: we are introducing potentially
a lot of new overloads for these operators, and we can't allow any to
create an ambiguity with existing overloads.
Helps #228, but we need more Magnitude support.