On 08/07/2020 16:02, Guido van Rossum wrote:
```
USE_POLAR = "polar"
USE_RECT = "rect"
```
Now we would like to be able to replace those literals with the
corresponding names throughout our code and have everything work like
before:
```
match t:
case (USE_RECT, real, imag):
return complex(real, imag)
case (USE_POLAR, r, phi):
return complex(r * cos(phi), r * sin(phi))
```
Alas, the compiler doesn’t know that we want `USE_RECT` to be a
constant value to be matched while we intend `real` and `imag` to be
variables to be given the corresponding values captured from the
subject. So various clever ways have been proposed to distinguish the
two cases.
I apologise for posting a second message re the same idea, but I can't
contain my enthusiasm for it:-)
and I want to make sure it's not overlooked:
*Use '==' to mark* (when necessary) *load-and-compare items*:
match t:
case (==USE_RECT, real, imag):
return complex(real, imag)
case (==USE_POLAR, r, phi):
return complex(r * cos(phi), r * sin(phi))
allowing incidentally a possible future extension to other relational
operators:
case Point(x, >YMAX):
case >= 42:
If this really is a deal-breaker after all other issues have been
settled, we could go back to considering some special markup for
load-and-compare of simple names (even though we expect this case to
be very rare). But there’s no pressing need to decide to do this now
-- we can always add new markup for this purpose in a future version,
as long as we continue to support dotted names without markup,
since that *is* a commonly needed case.
Except that if this idea were taken to its logical conclusion,
mod.var would be a capture variable (contrary to the PEP)
==mod.var would be a load-and-compare value
Which may be controversial, but seems to have more overall consistency.
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