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authorKen Raeburn2015-11-01 01:42:21 -0400
committerKen Raeburn2015-11-01 01:42:21 -0400
commit39372e1a1032521be74575bb06f95a3898fbae30 (patch)
tree754bd242a23d2358ea116126fcb0a629947bd9ec /admin/notes/iftc
parent6a3121904d76e3b2f63007341d48c5c1af55de80 (diff)
parente11aaee266da52937a3a031cb108fe13f68958c3 (diff)
downloademacs-39372e1a1032521be74575bb06f95a3898fbae30.tar.gz
emacs-39372e1a1032521be74575bb06f95a3898fbae30.zip
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1Iso-Functional Type Contour
2
3
4This is a term coined to describe "column int->float" change approach, and can
5be used whenever low-level types need to change (hopefully not often!) but the
6meanings of the values (whose type has changed) do not.
7
8The premise is that changing a low-level type potentially means lots of code
9needs to be changed as well, and the question is how to do this incrementally,
10which is the preferred way to change things.
11
12Say LOW and HIGH are C functions:
13
14 int LOW (void) { return 1; }
15 void HIGH (void) { int value = LOW (); }
16
17We want to convert LOW to return float, so we cast HIGH usage:
18
19 float LOW (void) { return 1.0; }
20 void HIGH (void) { int value = (int) LOW (); } /* iftc */
21
22The comment /* iftc */ is used to mark this type of casting to differentiate
23it from other casting. We commit the changes and can now go about modifying
24LOW and HIGH separately. When HIGH is ready to handle the type change, the
25cast can be removed.
26