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Prototype: Difference between revisions
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The '''prototype''' of an array is, in the [[nested array model]], an array which gives information about the type and structure of its [[element]]s. It is derived from the first element of the array in [[ravel order]], or, if the array is [[Empty array|empty]], from information stored alongside the array (usually this information is just the prototype itself). An array's prototype is used as a [[fill element]] for operations involving that array, and to determine some [[identity element]]s. | The '''prototype''' of an array is, in the [[nested array model]], an array which gives information about the type and structure of its [[element]]s. It is derived from the first element of the array in [[ravel order]], or, if the array is [[Empty array|empty]], from information stored alongside the array (usually this information is just the prototype itself). An array's prototype is used as a [[fill element]] for operations involving that array, and to determine some [[identity element]]s. | ||
== Examples == | == Examples == | ||
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</source> | </source> | ||
{{Works in|[[Dyalog APL]]}} | {{Works in|[[Dyalog APL]]}} | ||
== Support == | |||
A few dialects have [[Type]] as a [[primitive function]], and in those, the prototype is simply the type of the first element: | |||
<source lang=apl> | |||
⊤↑ (1 2 'ab') 3 4 | |||
┌─┬─┬──┐ | |||
│0│0│ │ | |||
└─┴─┴──┘ | |||
</source> | |||
{{Works in|[[NARS2000]]}} | |||
<source lang=apl> | |||
∊⊃ (1 2 'ab') 3 4 | |||
┌─┬─┬──┐ | |||
│0│0│ │ | |||
└─┴─┴──┘ | |||
</source> | |||
{{Works in|[[Dyalog APL]] with [[migration level]]<nowiki>=</nowiki>0}} | |||
However, an array's prototype can always be determined by reshaping the array to become empty, and then coercing out a fill element: | |||
<source lang=apl> | |||
⊃ 0 ⍴ (1 2 'ab') 3 4 | |||
┌─┬─┬──┐ | |||
│0│0│ │ | |||
└─┴─┴──┘ | |||
</source> | |||
{{Works in|[[Dyalog APL]] with [[migration level]]<nowiki>≥</nowiki>2, [[APL2]], [[APLX]]}} | |||
[https://tryapl.org/?a=%u2283%200%20%u2374%20%281%202%20%27ab%27%29%203%204&run Try it now!] | |||
<source lang=apl> | |||
⊃ 0 ⍴ (1 2 'ab') 3 4 | |||
┌─┬─┬──┐ | |||
│0│0│ │ | |||
└─┴─┴──┘ | |||
</source> | |||
{{Works in|[[Dyalog APL]] with [[migration level]]<nowiki>=</nowiki>1}} | |||
APLs with a [[flat array model]] do not typically store prototype information, instead using only the array's type ([[character]], [[numeric]], or [[Box|boxed]]) to determine its [[Fill element|fills]]. | |||
{{APL features}} | {{APL features}} | ||