Re: proposal: FOREACH-IN-ARRAY (probably for 9.2?)

2010/12/17 Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>:
> Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> writes:
>> 2010/12/17 Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>:
>>> Furthermore, it's underspecified: who's to say how many dimensions of
>>> the array are supposed to get sliced off?  There's no reasonable place
>>> to extend this syntax to specify that.  It will also be inconsistent
>>> for "foreach scalar in array" to iterate element-by-element no matter
>>> how many dimensions array has, while "foreach array in array" does
>>> something different from that.
>
>> it reduce just one dimension. Now I expect, and I think so it is
>> correct, so user knows a used dimension. Just doesn't know a data. So
>> user can to decide and fill correct type. The design strictly remove
>> any U.I. from design. So using a incorect type is bug.
>
> In other words, your proposal is error-prone to use, restricted in what
> it can do, and incapable of being extended later without breaking
> things.  If there is some redeeming social value to set against those
> problems, I'm not seeing it.
>
> What I think we should have is
>
>        FOREACH scalar-variable IN ARRAY array-expression
>
> which iterates element by element regardless of how many dimensions the
> array has.  Then there should be some other syntax for iterating over
> slices, and we should give some thought to being able to specify how
> "deep" the slice is.  I can definitely think of use cases for pulling
> off either 1 dimension at a time (so you get vectors) or N-1 dimensions
> at a time, and it's not out of the realm of reason to want intermediate
> cases.

I am not against

>
> Maybe
>
>        FOR_EACH scalar-variable IN ARRAY array-expression
>
>        FOR_SLICE array-variable [DEPTH n] IN ARRAY array-expression
>
> Or I guess you could use the same leading keyword if you make the depth
> specification mandatory for the slice case:
>
>        FOREACH scalar-variable IN ARRAY array-expression
>
>        FOREACH array-variable SLICE n IN ARRAY array-expression
>

I prefer FOREACH keyword. The syntax can be enhanced and I like a talk
about it. I am not sure if SLICE is good keyword for this, but I don't
know better - hope so native speakers can select well. I could to use
maybe "DIMENSIONS" ?

Regards

Pavel

> That might be a better idea since it avoids the inevitable argument over
> whether the default slice depth should be 1 dimension or N-1 dimensions.
>
>                        regards, tom lane
>