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improve doc about string (im)mutability

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Irmen de Jong 2021-05-19 00:15:17 +02:00
parent ba96a637be
commit ca1a8cd617
2 changed files with 16 additions and 11 deletions
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24
docs/source/programming.rst
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@ -318,14 +318,22 @@ read the syntax reference on strings.
For regular assignments you still need to use an explicit ``&`` (address-of) to take For regular assignments you still need to use an explicit ``&`` (address-of) to take
the address of the string or array. the address of the string or array.
.. caution:: .. note:: Strings and their (im)mutability
It's probably best to avoid changing the contents in strings and treat them as static.
This includes changing certain letters by index, or by assigning a new value, or by *String literals outside of a string variable's initialization value*,
modifying the string via other means for example ``substr`` function and its cousins. are considered to be "constant", i.e. the string isn't going to change
This is because the changes persist in memory. If your program exits and is restarted during the execution of the program. The compiler takes advantage of this in certain
(without reloading it from disk), it will then start working with the modified strings ways. For instance, multiple identical occurrences of a string literal are folded into
instead of the original ones! just one string allocation in memory. Examples of such strings are the string literals
The same is true for arrays! So be careful to (re)initialize them if needed. passed to a subroutine as arguments.
*Strings that aren't such string literals are considered to be unique*, even if they
are the same as a string defined elsewhere. This includes the strings assigned to
a string variable in its declaration! These kind of strings are not deduplicated and
are just copied into the program in their own unique part of memory. This means that
it is okay to treat those strings as mutable; you can safely change the contents
of such a string without destroying other occurrences (as long as you stay within
the size of the allocated string!)
Special types: const and memory-mapped Special types: const and memory-mapped

3
docs/source/todo.rst
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@ -5,9 +5,6 @@ TODO
- possible idea: option to mark vardecls 'shared' to indicate they should not be optimized away because they're shared with assembly code? - possible idea: option to mark vardecls 'shared' to indicate they should not be optimized away because they're shared with assembly code?
However: who even needs variables declared in prog8 code that are only used by assembly??? However: who even needs variables declared in prog8 code that are only used by assembly???
- github issue about strings and their immutability:
IMPROVE DOCUMENTATION ABOUT STRINGS AND DEDUP and (NON)IMMUTABILITY.
- test all examples (including imgviewer, assembler and petaxian) before release of the new version - test all examples (including imgviewer, assembler and petaxian) before release of the new version
- simplify cx16.joystick_get2() once this cx16 rom issue is resolved: https://github.com/commanderx16/x16-rom/issues/203 - simplify cx16.joystick_get2() once this cx16 rom issue is resolved: https://github.com/commanderx16/x16-rom/issues/203