Re: Use C99 designated initializers for some structs

> On Aug 29, 2018, at 1:51 PM, David Steele <david@pgmasters.net> wrote:
>
> On 8/29/18 5:14 AM, Peter Eisentraut wrote:
>> On 29/08/2018 12:13, Peter Eisentraut wrote:
>>> Here is a patch to change some struct initializations to use C99-style
>>> designated initializers.  These are just a few particularly egregious
>>> cases that were hard to read and write, and error prone because of many
>>> similar adjacent types.
>>>
>>> (The PL/Python changes currently don't compile with Python 3 because of
>>> the situation described in the parallel thread "PL/Python: Remove use of
>>> simple slicing API".)
>>>
>>> Thoughts?
>
> +1.  This is an incredible win for readability/maintainability.

I tried doing this perhaps a year ago, and there are a few files with arrays
of structs whose representations get much larger when you change the format
in this way.  For instance, in guc.c:

static struct config_bool ConfigureNamesBool[] =
{
    {
        {"enable_seqscan", PGC_USERSET, QUERY_TUNING_METHOD,
            gettext_noop("Enables the planner's use of sequential-scan plans."),
            NULL
        },
        &enable_seqscan,
        true,
        NULL, NULL, NULL
    },

becomes:

static struct config_bool ConfigureNamesBool[] =
{
    {
        .gen = {
            .name = "enable_seqscan",
            .context = PGC_USERSET,
            .group = QUERY_TUNING_METHOD,
            .short_desc = gettext_noop("Enables the planner's use of sequential-scan plans."),
            .long_desc = NULL
        },
        .variable = &enable_seqscan,
        .boot_val = true,
        .check_hook = NULL,
        .assign_hook = NULL,
        .show_hook = NULL
    },

and then gets much longer if you do as per Tom's general suggestion and make
each field explicit (though Tom might not apply that rule to this case):

static struct config_bool ConfigureNamesBool[] =
{
    {
        .gen = {
            .name = "enable_seqscan",
            .context = PGC_USERSET,
            .group = QUERY_TUNING_METHOD,
            .short_desc = gettext_noop("Enables the planner's use of sequential-scan plans."),
            .long_desc = NULL,
            .flags = 0,
            .vartype = 0,
            .status = 0,
            .source = 0,
            .reset_source = 0,
            .scontext = 0,
            .reset_scontext = 0,
            .stack = NULL,
            .extra = NULL,
            .sourcefile = NULL,
            .sourceline = 0
        },
        .variable = &enable_seqscan,
        .boot_val = true,
        .check_hook = NULL,
        .assign_hook = NULL,
        .show_hook = NULL,
        .reset_val = false,
        .reset_extra = NULL
    },

This sort of thing happens an awful lot in guc.c, but it comes up in syscache.c
also, and perhaps other places, though I don't recall any longer which other files
were like this.

What should the general rule be for initializing arrays of structs such as these?

mark