forked from mpusz/mp-units
42 lines
1.0 KiB
ReStructuredText
42 lines
1.0 KiB
ReStructuredText
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.. namespace:: units
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Working with Legacy Interfaces
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==============================
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In case we are working with a legacy/unsafe interface we may be forced to
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extract a :term:`value of a quantity` with :func:`quantity::count()` and
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pass it to the library's output:
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.. code-block::
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:caption: legacy.h
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namespace legacy {
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void print_eta(double speed_in_mps);
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} // namespace legacy
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.. code-block::
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#include "legacy.h"
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#include <units/physical/si/velocity.h>
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using namespace units;
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constexpr Velocity auto avg_speed(Length auto d, Time auto t)
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{
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return d / t;
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}
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void print_eta(Length auto d, Time auto t)
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{
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Velocity auto v = avg_speed(d, t);
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legacy::print_eta(quantity_cast<si::metre_per_second>(v).count());
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}
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.. important::
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When dealing with a quantity of an unknown ``auto`` type please remember
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to always use `quantity_cast` to cast it to a desired unit before calling
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`quantity::count()` and passing the raw value to the legacy/unsafe interface.
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