Add stream to array conversion function to standard lib

[Shadow-Devil]

Description: This Stackoverflow question says, that there are two ways to convert a stream to an array, but in my opinion both of them seem quite verbose.

It would be great to have a stream:toArray() function, which is the opposite of array:toStream() and would convert a stream to an array. In the documentation of the function it should be noted, that for infinite streams this will loop forever.

What do you think about this?

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[jclark]

I think that's a good addition.

One question is can we write the type for this.

public isolated function toArray(stream<T,E|()>) returns E|T[] = external;

Would that work @MaryamZi ?

[MaryamZi]

I also agree that this would be a good addition. Especially with database clients, we often see functions/query expressions introduced to do just this.

One question is can we write the type for this.

public isolated function toArray(stream<T,E|()>) returns E|T[] = external;

Would that work @MaryamZi ?

I believe this should work, similar to stream:reduce, which is defined as

@typeParam
type Type any|error;

@typeParam
type Type1 any|error;

@typeParam
type ErrorType error;

public isolated function reduce(stream<Type,ErrorType?> stm, 
         @isolatedParam function(Type1 accum, Type val) returns Type1 func, Type1 initial)
   returns Type1|ErrorType = external;

(We do seem to have a bug with stream:reduce type checking in the jBallerina implementation when the completion type is a subtype of error - https://github.com/ballerina-platform/ballerina-lang/issues/43209)