new 'fake-variable' declare syntax: "alias/alias_name = value"

ID:2960394
 
Jan 14, 5:00 pm (Edited on Jan 14, 5:30 pm)
Applies to:
Status: Open
Issue hasn't been assigned a status value.
alias is a kind of var declaration, but its nature is closer to macro

see an example below:
/datum/race/proc/get_magic_types()
    return null

/datum/race/human/get_magic_types()
    alias/approved_magic_types = list("fire", "ice")
    return approved_magic_types

/datum/race/elf/get_magic_types()
    // #define MAGIC_TYPES list("earth", "plant")
    // return MAGIC_TYPES
    alias/approved_magic_types = list("earth", "plant")
    return approved_magic_types


another sample:
/datum/proc/check_available()
    if( proc_a() && proc_b() && src.this_okay && proc_c() && proc_d() || proc_all_pass() )
      return 1
    return 0
// long if condition. ugly.

#define CAN_CAST_MAGIC (proc_a() && proc_b() && src.this_okay && proc_c() && proc_d() || proc_all_pass())
/datum/proc/check_available_with_macro()
    if(CAN_CAST_MAGIC)
        return 1
    return 0
// it reads better because you know the context of the if condition, but macro? cringe

/datum/proc/check_available_with_alias()
    alias/can_cast_magic = proc_a() && proc_b() && src.this_okay && proc_c() && proc_d() || proc_all_pass()
    return can_cast_magic
// this reads perfectly sane.


I'd like to elaborate the last proc.
/datum/proc/check_available_with_alias()
    alias/can_cast_magic = proc_a() && proc_b() && src.this_okay && proc_c() && proc_d() || proc_all_pass()
    return can_cast_magic

this is actually the same below:
/datum/proc/check_available_with_alias()
#define can_cast_magic (proc_a() && proc_b() && src.this_okay && proc_c() && proc_d() || proc_all_pass())
    return can_cast_magic
#undef can_cast_magic

and that becomes:
/datum/proc/check_available_with_alias()
    return (proc_a() && proc_b() && src.this_okay && proc_c() && proc_d() || proc_all_pass())


What we can get:
- this works like a semi-macro, so it doesn't occupy variable memory
- you can have a same name in multiple area, not doing #undef and #def every time.
- you can give a name to a condition instead of contextless verbose in the if condition


Why do we want this?:
/datum/proc/check_available()
    return proc_a() && proc_b() && src.this_okay && proc_c() && proc_d() || proc_all_pass()

This is contextless, so we might want to do this:

/datum/proc/check_available()
    var/can_cast_magic = proc_a() && proc_b() && src.this_okay && proc_c() && proc_d() || proc_all_pass()
    return can_cast_magic

but this takes a variable. we might want to return the value directly without saving it.



< Alias behavior >
- you can write alias in /datum as if it has variables, but this will not be saved as a variable.
For example, when `/mob/alias/check_client = { if(src.client) {return src.client;} else {return global.fake_client;} }` is defined, this `check_client` is accessible from all mob procs. (but I am not sure this is a good idea... proc alias seems fine to me, but not this) ---> I think alias should be only allowed in proc codes.
- you can undef alias by doing "alias/alias_name = null"
- assigning values to an alias should be always done with "alias/alias_name = value" syntax, not omitting "alias/" part, because it is not a real variable.
- alias does not exist in runtime because it's deconstructed to what's stated.

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