59 lines
1.9 KiB
Text
59 lines
1.9 KiB
Text
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#lang scribble/manual
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@(require (for-label racket))
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@title{Scoping and Closure}
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scoping of variables@section{categories}
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Language
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SuperCollider has nested scoping of variables. A function can refer not only to its own arguments and variables, but also to those declared in any enclosing (defining) contexts.
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For example, the function defined below within makeCounter can access all of the arguments and variables declared in
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@racketblock[makeCounter::.
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Other code can call the returned function at some later time and it can access and update the values contained in ]
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@racketblock[makeCounter:: at the time when the inner function was instantiated.
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]
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@racketblock[
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(
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var makeCounter;
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makeCounter = { arg curVal=0, stepVal=1;
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// return a function :
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{
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var temp;
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// temp is local to this function, curVal & stepVal in the
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// enclosing function are referred to here within.
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temp = curVal;
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curVal = curVal + stepVal;
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temp // return result
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}
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};
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// Each invocation of makeCounter creates a new set of variables curVal and stepVal:
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x = makeCounter.value(10, 1);
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z = makeCounter.value(99, 100);
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)
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::
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x and z are functions which refer to different instances of the variables curVal and stepVal
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]
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@racketblock[
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x.value.postln; // posts 10
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x.value.postln; // posts 11
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z.value.postln; // posts 99
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z.value.postln; // posts 199
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x.value.postln; // posts 12
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x.value.postln; // posts 13
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z.value.postln; // posts 299
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z.value.postln; // posts 399
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::
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Note that even though the function which defines curVal and stepVal has completed execution, its variables are still accessible to those functions that were defined within its context.
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This is known as lexical closure, the capturing and availability of variables defined in outer contexts by inner contexts even when the outer contexts may have completed execution.
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]
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