text: global address; url: exec/runtime.html#syntax-globaladdr

url: syntax/types.html#syntax-mut

text: var

text: const

* The <dfn>Global object cache</dfn>, mapping [=global address=]es to {{Global}} objects.

1. If |externtype| is of the form [=𝗀𝗅𝗈𝖻𝖺𝗅=] |mut| |valtype|,

1. If [=Type=](|v|) is [=Number=],

1. If |valtype| is [=𝗂𝟨𝟦=], throw a {{LinkError}} exception.

1. Let |value| be [=ToWebAssemblyValue=](|v|, |valtype|)

1. Let |store| be the [=surrounding agent=]'s [=associated store=].

1. Let (|store|, |globaladdr|) be [=alloc_global=](|store|, [=const=] |valtype|, |value|).

1. Set the [[surrounding agent=]'s [=associated store=] to |store|.

1. If |v| is a {{Global}} instance,

1. Let |globaladdr| be |v|.\[[Global]]

1. Otherwise,

1. Throw a {{LinkError}} exception.

1. Let |global| be [=create a global object|a new Global object=] created from |globaladdr|.

1. Let |value| be |global|.

dictionary GlobalDescriptor {

required USVString value;

boolean mutable = false;

};

interface Global {

unrestricted double valueOf();

attribute unrestricted double value;

};

A {{Global}} object represents a single [=global instance=]

which can be simultaneously referenced by multiple {{Instance}} objects. Each

{{Global}} object has one internal slot:

* \[[Global]] : a [=global address=]

To <dfn>create a global object</dfn> from a [=global address=] |globaladdr|, perform the following steps:

1. Let |map| be the current [=agent=]'s associated [=Global object cache=].

1. If |map|[|globaladdr|] [=map/exists=],

1. Return |map|[|globaladdr|].

1. Let |global| be a new {{Global}} instance with \[[Global]] set to |globaladdr|.

1. [=map/Set=] |map|[|globaladdr|] to |global|.

1. Return |global|.

The algorithm <dfn>ToValueType</dfn>(|s|) performs the following steps:

1. If |s| equals "i32", return [=𝗂𝟥𝟤=].

1. If |s| equals "f32", return [=𝖿𝟥𝟤=].

1. If |s| equals "f64", return [=𝖿𝟨𝟦=].

1. Otherwise, throw a {{TypeError}} exception.

The <dfn constructor for="Global">Global(descriptor, v)</dfn> constructor, when invoked, performs the following steps:

1. Let |mutable| be |descriptor|["mutable"].

1. Let |valuetype| be [=ToValueType=](|descriptor|["value"]).

1. Let |value| be [=ToWebAssemblyValue=](|v|, |valuetype|).

1. If |mutable| is true, let |globaltype| be [=var=] |valuetype|; otherwise, let |globaltype| be [=const=] |valuetype|.

1. Let |store| be the current agent's [=associated store=].

1. Let (|store|, |globaladdr|) be [=alloc_global=](|store|, |globaltype|, |value|). <!-- TODO(littledan): Report allocation failure https://github.com/WebAssembly/spec/issues/584 -->

1. Set the current agent's [=associated store=] to |store|.

1. [=Create a global object=] from the global address |globaladdr| and return the result.

The algorithm <dfn>GetGlobalValue</dfn>({{Global}} |global|) performs the following steps:

1. Let |store| be the current agent's [=associated store=].

1. Let |globaladdr| be |global|.\[[Global]].

1. Let |globaltype| be [=type_global=](|store|, |globaladdr|).

1. If |globaltype| is of the form |mut| [=𝗂𝟨𝟦=], throw a {{TypeError}}.

1. Let |value| be [=read_global=](|store|, |globaladdr|).

1. Return [=ToJSValue=](|value|).

The getter of the <dfn attribute for="Global">value</dfn> attribute of {{Global}}, when invoked, performs the following steps:

1. Let |global| be the {{Global}} instance.

1. Return [=GetGlobalValue=](|global|).

The setter of the value attribute of {{Global}}, when invoked with a value |v|, performs the following steps:

1. Let |global| be the {{Global}} instance.

1. Let |store| be the current agent's [=associated store=].

1. Let |globaladdr| be |global|.\[[Global]].

1. Let |globaltype| be [=type_global=](|store|, |globaladdr|), where |globaltype| is of the form |mut| |valuetype|.

1. If |mut| is [=const=], throw a {{TypeError}.

1. If |valuetype| is [=𝗂𝟨𝟦=], throw a {{TypeError}}.

1. Let |value| be [=ToWebAssemblyValue=](|v|, |valuetype|).

1. Let |store| be [=write_global=](|store|, |globaladdr|, |value|).

1. If |store| is [=error=], throw a {{RangeError}} exception.

1. Set the current agent's [=associated store=] to |store|.

The <dfn method for="Global">valueOf()</dfn> method, when invoked, performs the following steps:

1. Let |global| be the {{Global}} instance.

1. Return [=GetGlobalValue=](|global|).

" let v = instance.exports[name];\n" ^

" return (v instanceof WebAssembly.Global) ? v.value : v;\n" ^

| GlobalExport x -> ignore (global c x)

(module (global (mut f32) (f32.const 0)) (export "a" (global 0)))

(module (global (export "a") (mut f32) (f32.const 0)))

;; export mutable globals

(global $mut_glob (export "mut_glob") (mut i32) (i32.const 142))

(func (export "get_mut") (result i32) (get_global $mut_glob))

(func (export "set_mut") (param i32) (set_global $mut_glob (get_local 0)))

(global $mut_glob (import "Mg" "mut_glob") (mut i32))

(func $get_mut (import "Mg" "get_mut") (result i32))

(func $set_mut (import "Mg" "set_mut") (param i32))

(export "Mg.mut_glob" (global $mut_glob))

(export "Mg.get_mut" (func $get_mut))

(export "Mg.set_mut" (func $set_mut))

(assert_return (get $Mg "mut_glob") (i32.const 142))

(assert_return (get $Ng "Mg.mut_glob") (i32.const 142))

(assert_return (invoke $Mg "get_mut") (i32.const 142))

(assert_return (invoke $Ng "Mg.get_mut") (i32.const 142))

(assert_return (invoke $Mg "set_mut" (i32.const 241)))

(assert_return (get $Mg "mut_glob") (i32.const 241))

(assert_return (get $Ng "Mg.mut_glob") (i32.const 241))

(assert_return (invoke $Mg "get_mut") (i32.const 241))

(assert_return (invoke $Ng "Mg.get_mut") (i32.const 241))

(assert_unlinkable

(module (import "Mg" "mut_glob" (global i32)))

"incompatible import type"

)

(assert_unlinkable

(module (import "Mg" "glob" (global (mut i32))))

"incompatible import type"

)

addImportedGlobal(module = "", name, type, mutable = false) {

mutable: mutable}