On Thursday, 26 May 2016 at 02:17:20 UTC, Observer wrote:
On Wednesday, 25 May 2016 at 17:08:02 UTC, Martin Tschierschke
wrote:
A newbee question about language design:
When I looked first time at Ruby I liked the simple a,b = b,a
syntax,
so swap. Would it be theoretically possible to allow this?
And if not, where does it breaks the general language design?
There's something about this notation that immediately makes
me think more generally. swap is just the degenerate form
of a more-general circular-shift operation in two different
dimensions. This form assumes that the shifting stops after
only
a single shift position (or more generally, that the number of
shift positions is odd); and having just two operands makes it
unnecessary to specify whether the shifting is to the left or to
the right. But even a circular-shift operation is itself just a
degenerate form of a more-general arbitrary-permutation
operation.
Other permutations have common applicability in computer
science,
such as the bit-reversed addressing used on DSP chips to support
butterfly operations in FFT (actually, DFT) algorithms. All of
which makes me wonder: if we want to generalize swap, should
we go
farther than just one algorithmic stage? How about a very
general
routine that accepts a permutation mapping and a set of
arguments,
and scrambles the arguments according to the mapping?
There's indexed, but it doesn't swap - it only provides access
based on your permutation and only works if all data has a
CommonType.
http://dlang.org/phobos/std_range.html#.indexed
For what it's worth, it's pretty cool to build rangified swaps of
ranges - e.g. in combinatorics:
http://docs.mir.dlang.io/latest/mir_combinatorics.html
