Raku Land

JSON::Fast

cpan:TIMOTIMO

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JSON::Fast

A naive imperative JSON parser in pure Raku (but with direct access to nqp:: ops), to evaluate performance against JSON::Tiny. It is a drop-in replacement for JSON::Tiny’s from-json and to-json subs, but it offers a few extra features.

Currently it seems to be about 4x faster and uses up about a quarter of the RAM JSON::Tiny would use.

This module also includes a very fast to-json function that tony-o created and lizmat later completely refactored.

Exported subroutines

to-json

    my $*JSON_NAN_INF_SUPPORT = 1; # allow NaN, Inf, and -Inf to be serialized.
    say to-json [<my Raku data structure>];
    say to-json [<my Raku data structure>], :!pretty;
    say to-json [<my Raku data structure>], :spacing(4);

enum Blerp <Hello Goodbye>;
say to-json [Hello, Goodbye]; # ["Hello", "Goodbye"]
say to-json [Hello, Goodbye], :enums-as-value; # [0, 1]

Encode a Raku data structure into JSON. Takes one positional argument, which is a thing you want to encode into JSON. Takes these optional named arguments:

pretty

Bool. Defaults to True. Specifies whether the output should be "pretty", human-readable JSON. When set to false, will output json in a single line.

spacing

Int. Defaults to 2. Applies only when pretty is True. Controls how much spacing there is between each nested level of the output.

sorted-keys

Bool, defaults to False. Specifies whether keys from objects should be sorted before serializing them to a string or if $obj.keys is good enough.

enum-as-value

Bool, defaults to False. Specifies whether enums should be json-ified as their underlying values, instead of as the name of the enum.

from-json

    my $x = from-json '["foo", "bar", {"ber": "bor"}]';
    say $x.perl;
    # outputs: $["foo", "bar", {:ber("bor")}]

Takes one positional argument that is coerced into a Str type and represents a JSON text to decode. Returns a Raku datastructure representing that JSON.

immutable

Bool. Defaults to False. Specifies whether Hashes and Arrays should be rendered as immutable datastructures instead (as Map / List. Creating an immutable data structures is mostly saving on memory usage, and a little bit on CPU (typically around 5%).

This also has the side effect that elements from the returned structure can now be iterated over directly because they are not containerized.

    my %hash := from-json "META6.json".IO.slurp, :immutable;
    say "Provides:";
    .say for %hash<provides>;

Additional features

Adapting defaults of "from-json"

In the use statement, you can add the string "immutable" to make the default of the immutable parameter to the from-json subroutine True, rather than False.

    use JSON::Fast <immutable>;  # create immutable data structures by default

Adapting defaults of "to-json"

In the use statement, you can add the strings "!pretty", "sorted-keys" and/or "enums-as-value" to change the associated defaults of the to-json subroutine.

    use JSON::FAST <!pretty sorted-keys enums-as-value>;

Strings containing multiple json pieces

When the document contains additional non-whitespace after the first successfully parsed JSON object, JSON::Fast will throw the exception X::JSON::AdditionalContent. If you expect multiple objects, you can catch that exception, retrieve the parse result from its parsed attribute, and remove the first rest-position characters off of the string and restart parsing from there.