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Add fromArray method to Buffer #368

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Add fromArray method to Buffer #368

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15 changes: 15 additions & 0 deletions src/Buffer.mo
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Original file line number Diff line number Diff line change
Expand Up @@ -146,4 +146,19 @@ module {
};
};

/// Construct a buffer from an array.
public func fromArray<T>(arr: [T]): Buffer<T> {
let count = arr.size();
let buffer = Buffer<T>(count);

var i = 0;
label l loop {
if (i >= count) break l;
buffer.add(arr[i]);
i += 1;
};

buffer
};
Comment on lines +149 to +162
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@nomeata nomeata Apr 26, 2022

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Thanks! Why not simply

Suggested change
/// Construct a buffer from an array.
public func fromArray<T>(arr: [T]): Buffer<T> {
let count = arr.size();
let buffer = Buffer<T>(count);
var i = 0;
label l loop {
if (i >= count) break l;
buffer.add(arr[i]);
i += 1;
};
buffer
};
/// Construct a buffer from an array.
public func fromArray<T>(arr: [T]): Buffer<T> {
return { count = arr.size(); elems = Array.thaw(arr) }
}

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@xlaywan xlaywan Apr 26, 2022

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Looks definitely better!
But can it create an instance of the Buffer class? Motoko Playground shows error:
image

It was intended to be a static method like let buf = Buffer.fromArray<Nat>([1, 2, 3]);
Probably it will work as an instance method like:

let buf = Buffer.Buffer<Nat>(0);
buf.fromArray([1, 2, 3]);

image

Not sure we can leave the name fromArray in this case, because in other files in base lib from* methods are static.

Link to the playground https://m7sm4-2iaaa-aaaab-qabra-cai.raw.ic0.app/?tag=2337373062

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@nomeata nomeata Apr 26, 2022

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Ah, right, Motoko classes have only one constructor usually…

Maybe first add buffer.addArray (which can be implemented efficiently using Array.thraw, especially if the buffer is empty before), and then the fromArray function.


}