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Date: Tue, 27 Dec 2011 08:05:18 +1100
Subject: Re: Pythonification of the asterisk-based collection packing/unpacking syntax
From: Chris Angelico <rosuav@gmail.com>
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Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:17981

On Tue, Dec 27, 2011 at 7:58 AM, Eelco <hoogendoorn.eelco@gmail.com> wrote:
> What you are talking about goes by the name of a 'dynamic type CHECK';
> some kind of syntactic sugar for something like
> 'assert(type(obj)==sometype)'. Like a 'type cast', this is also a
> runtime concept...
>
> By contrast, here is the first google hit for 'type constraint'.
>
> http://msdn.microsoft.com/en-us/library/d5x73970.aspx
>
> "...you can apply restrictions to the kinds of types ... by using a
> type that is not allowed by a constraint, the result is a COMPILE-TIME
> ERROR" (emphasis mine)

A constraint can be applied at compile time or at run time. It'd be
valid to apply them at edit time, if you so chose - your editor could
refuse to save your file until you fix the problem. Doesn't mean a
thing. Python, by its nature, cannot do compile-time type checking.
Under no circumstances, however, does this justify the use of the term
"constraint" to mean "utterly different semantics of the same code".

ChrisA