[Issue 17979] New: Improve documentation for lazy parameters

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=17979

          Issue ID: 17979
           Summary: Improve documentation for lazy parameters
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: dlang.org
          Assignee: nobody at puremagic.com
          Reporter: crimaniak at gmail.com

Lazy parameters in fact implemented using delegates and affect @nogc
possibility. I propose additions to documentation:

https://dlang.org/spec/function.html#parameters section

It needs to write that the delegate is used, and explicitly document what
exactly happens in the case of several occurrences of the used parameter -
whether the delegate is called each time, or only the first, and then the
returned value is used (affects non-pure lazy parameters).

https://dlang.org/spec/garbage.html#op_involving_gc

It will be useful to mention lazy parameters in this list too.

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