Components¶
Sorts¶
A component’s definitions define objects, each of which is of one of the following sorts:
\[\begin{split}\begin{array}{llcl}
\def\mathdef2256#1{{}}\mathdef2256{(coresort)} & \href{../syntax/components.html#syntax-coresort}{\mathit{core{:}sort}} &::=&
\href{../syntax/components.html#syntax-coresort}{\mathsf{func}} | \href{../syntax/components.html#syntax-coresort}{\mathsf{table}} | \href{../syntax/components.html#syntax-coresort}{\mathsf{memory}} | \href{../syntax/components.html#syntax-coresort}{\mathsf{global}} | \href{../syntax/components.html#syntax-coresort}{\mathsf{type}} | \href{../syntax/components.html#syntax-coresort}{\mathsf{module}} | \href{../syntax/components.html#syntax-coresort}{\mathsf{instance}}\\
\def\mathdef2256#1{{}}\mathdef2256{(sort)} & \href{../syntax/components.html#syntax-sort}{\mathit{sort}} &::=&
\href{../syntax/components.html#syntax-sort}{\mathsf{core}}~\href{../syntax/components.html#syntax-coresort}{\mathit{core{:}sort}}\\&&|&
\href{../syntax/components.html#syntax-sort}{\mathsf{func}} | \href{../syntax/components.html#syntax-sort}{\mathsf{value}} | \href{../syntax/components.html#syntax-sort}{\mathsf{type}} | \href{../syntax/components.html#syntax-sort}{\mathsf{component}} | \href{../syntax/components.html#syntax-sort}{\mathsf{instance}}
\end{array}\end{split}\]
Indices¶
Each object defined by a component exists within an index space made up of all objects of the same sort. Unlike in Core WebAssembly, a component definition may only refer to objects that were defined prior to it in the current component. Future definitions refer to past definitions by means of an index into the appropriate index space:
\[\begin{split}\begin{array}{llll}
\def\mathdef2256#1{{}}\mathdef2256{(coremoduleidx)} & \href{../syntax/components.html#syntax-coremoduleidx}{\mathit{core{:}moduleidx}} &::=& \href{../syntax/values.html#syntax-int}{\mathit{u32}}\\
\def\mathdef2256#1{{}}\mathdef2256{(coreinstanceidx)} & \href{../syntax/components.html#syntax-coreinstanceidx}{\mathit{core{:}instanceidx}} &::=& \href{../syntax/values.html#syntax-int}{\mathit{u32}}\\
\def\mathdef2256#1{{}}\mathdef2256{(componentidx)} & \href{../syntax/components.html#syntax-componentidx}{\mathit{componentidx}} &::=& \href{../syntax/values.html#syntax-int}{\mathit{u32}}\\
\def\mathdef2256#1{{}}\mathdef2256{(instanceidx)} & \href{../syntax/components.html#syntax-instanceidx}{\mathit{instanceidx}} &::=& \href{../syntax/values.html#syntax-int}{\mathit{u32}}\\
\def\mathdef2256#1{{}}\mathdef2256{(funcidx)} & \href{../syntax/components.html#syntax-funcidx}{\mathit{funcidx}} &::=& \href{../syntax/values.html#syntax-int}{\mathit{u32}}\\
\def\mathdef2256#1{{}}\mathdef2256{(corefuncidx)} & \href{../syntax/components.html#syntax-corefuncidx}{\mathit{core{:}funcidx}} &::=& \href{../syntax/values.html#syntax-int}{\mathit{u32}}\\
\def\mathdef2256#1{{}}\mathdef2256{(valueidx)} & \href{../syntax/components.html#syntax-valueidx}{\mathit{valueidx}} &::=& \href{../syntax/values.html#syntax-int}{\mathit{u32}}\\
\def\mathdef2256#1{{}}\mathdef2256{(typeidx)} & \href{../syntax/components.html#syntax-typeidx}{\mathit{typeidx}} &::=& \href{../syntax/values.html#syntax-int}{\mathit{u32}}\\
\def\mathdef2256#1{{}}\mathdef2256{(coretypeidx)} & \href{../syntax/components.html#syntax-coretypeidx}{\mathit{core{:}typeidx}} &::=& \href{../syntax/values.html#syntax-int}{\mathit{u32}}
\end{array}\end{split}\]
\[\begin{split}\begin{array}{llll}
\def\mathdef2256#1{{}}\mathdef2256{(coresortidx)} & \href{../syntax/components.html#syntax-coresortidx}{\mathit{core{:}sortidx}} &::=& \{ \href{../syntax/components.html#syntax-coretypeidx}{\mathsf{sort}}~\href{../syntax/components.html#syntax-coresort}{\mathit{core{:}sort}}, \href{../syntax/components.html#syntax-coretypeidx}{\mathsf{idx}}~\href{../syntax/values.html#syntax-int}{\mathit{u32}} \}\\
\def\mathdef2256#1{{}}\mathdef2256{(sortidx)} & \href{../syntax/components.html#syntax-sortidx}{\mathit{sortidx}} &::=& \{ \href{../syntax/components.html#syntax-sortidx}{\mathsf{sort}}~\href{../syntax/components.html#syntax-sort}{\mathit{sort}}, \href{../syntax/components.html#syntax-sortidx}{\mathsf{idx}}~\href{../syntax/values.html#syntax-int}{\mathit{u32}} \}
\end{array}\end{split}\]
Definitions¶
Each object within a component is defined by a definition, of which there are several kinds:
\[\begin{split}\begin{array}{llcl}
\def\mathdef2256#1{{}}\mathdef2256{(definition)} & \href{../syntax/components.html#syntax-definition}{\mathit{definition}} &::=&
\href{../syntax/components.html#syntax-definition}{\mathsf{core\_module}}~\href{https://webassembly.github.io/spec/core/syntax/modules.html#syntax-module}{\mathit{core{:}}\mathit{module}}\\&&|&
\href{../syntax/components.html#syntax-definition}{\mathsf{core\_instance}}~\href{../syntax/components.html#syntax-coreinstance}{\mathit{core{:}instance}}\\&&|&
\href{../syntax/components.html#syntax-definition}{\mathsf{core\_type}}~\href{../syntax/types.html#syntax-coredeftype}{\mathit{core{:}deftype}}\\&&|&
\href{../syntax/components.html#syntax-definition}{\mathsf{component}}~\href{../syntax/components.html#syntax-component}{\mathit{component}}\\&&|&
\href{../syntax/components.html#syntax-definition}{\mathsf{instance}}~\href{../syntax/components.html#syntax-instance}{\mathit{instance}}\\&&|&
\href{../syntax/components.html#syntax-definition}{\mathsf{alias}}~\href{../syntax/types.html#syntax-alias}{\mathit{alias}}\\&&|&
\href{../syntax/components.html#syntax-definition}{\mathsf{type}}~\href{../syntax/types.html#syntax-deftype}{\mathit{deftype}}\\&&|&
\href{../syntax/components.html#syntax-definition}{\mathsf{canon}}~\href{../syntax/components.html#syntax-canon}{\mathit{canon}}\\&&|&
\href{../syntax/components.html#syntax-definition}{\mathsf{start}}~\href{../syntax/components.html#syntax-start}{\mathit{start}}\\&&|&
\href{../syntax/components.html#syntax-definition}{\mathsf{import}}~\href{../syntax/components.html#syntax-import}{\mathit{import}}\\&&|&
\href{../syntax/components.html#syntax-definition}{\mathsf{export}}~\href{../syntax/components.html#syntax-export}{\mathit{export}}\\
\end{array}\end{split}\]
Core instances¶
A core instance may be defined either by instantiating a core module with other core instances taking the place of its first-level imports, or by creating a core module from whole cloth by combining core definitions already present in our index space:
\[\begin{split}\begin{array}{llcl}
\def\mathdef2256#1{{}}\mathdef2256{(coreinstance)} & \href{../syntax/components.html#syntax-coreinstance}{\mathit{core{:}instance}} &::=&
\href{../syntax/components.html#syntax-coreinstance}{\mathsf{instantiate}}~\href{../syntax/components.html#syntax-coremoduleidx}{\mathit{core{:}moduleidx}}~\href{../syntax/components.html#syntax-coreinstantiatearg}{\mathit{core{:}instantiatearg}}^{*}\\&&|&
\href{../syntax/components.html#syntax-coreinstance}{\mathsf{exports}}~\href{../syntax/components.html#syntax-coreexport}{\mathit{core{:}export}}^{*}\\
\def\mathdef2256#1{{}}\mathdef2256{(coreinstantiatearg)} & \href{../syntax/components.html#syntax-coreinstantiatearg}{\mathit{core{:}instantiatearg}} &::=&
\{ \href{../syntax/components.html#syntax-coreinstantiatearg}{\mathsf{name}}~\href{../syntax/values.html#syntax-name}{\mathit{name}}, \href{../syntax/components.html#syntax-coreinstantiatearg}{\mathsf{instance}}~\href{../syntax/components.html#syntax-coreinstanceidx}{\mathit{core{:}instanceidx}} \}\\
\def\mathdef2256#1{{}}\mathdef2256{(coreexport)} & \href{../syntax/components.html#syntax-coreexport}{\mathit{core{:}export}} &::=& \{ \href{../syntax/components.html#syntax-coreexport}{\mathsf{name}}~\href{../syntax/values.html#syntax-name}{\mathit{name}}, \href{../syntax/components.html#syntax-coreexport}{\mathsf{def}}~\href{../syntax/components.html#syntax-coresortidx}{\mathit{core{:}sortidx}} \}\\
\end{array}\end{split}\]
Components¶
A component is merely a sequence of definitions:
\[\begin{array}{llll}
\def\mathdef2256#1{{}}\mathdef2256{(component)} & \href{../syntax/components.html#syntax-component}{\mathit{component}} &::=& \href{../syntax/components.html#syntax-definition}{\mathit{definition}}^{*}
\end{array}\]
Instances¶
Component-level instance declarations are nearly identical to core-level instance declarations, with the caveat that more sorts of definitions may be supplied as imports:
\[\begin{split}\begin{array}{llcl}
\def\mathdef2256#1{{}}\mathdef2256{(instance)} & \href{../syntax/components.html#syntax-instance}{\mathit{instance}} &::=&
\href{../syntax/components.html#syntax-instance}{\mathsf{instantiate}}~\href{../syntax/components.html#syntax-componentidx}{\mathit{componentidx}}~\href{../syntax/components.html#syntax-instantiatearg}{\mathit{instantiatearg}}^{*}\\&&|&
\href{../syntax/components.html#syntax-instance}{\mathsf{exports}}~\href{../syntax/components.html#syntax-export}{\mathit{export}}^{*}\\
\def\mathdef2256#1{{}}\mathdef2256{(instantiatearg)} & \href{../syntax/components.html#syntax-instantiatearg}{\mathit{instantiatearg}} &::=&
\{ \href{../syntax/components.html#syntax-instantiatearg}{\mathsf{name}}~\href{../syntax/values.html#syntax-name}{\mathit{name}}, \href{../syntax/components.html#syntax-instantiatearg}{\mathsf{arg}}~\href{../syntax/components.html#syntax-sortidx}{\mathit{sortidx}} \}
\end{array}\end{split}\]
Aliases¶
An alias definition copies a definition from some other module, component, or instance into an index space of the current component:
\[\begin{split}\begin{array}{llcl}
\def\mathdef2256#1{{}}\mathdef2256{(alias)} & \href{../syntax/types.html#syntax-alias}{\mathit{alias}} &::=& \{ \href{../syntax/types.html#syntax-alias}{\mathsf{sort}}~\href{../syntax/components.html#syntax-sort}{\mathit{sort}}, \href{../syntax/types.html#syntax-alias}{\mathsf{target}}~\href{../syntax/components.html#syntax-aliastarget}{\mathit{aliastarget}} \}\\
\def\mathdef2256#1{{}}\mathdef2256{(aliastarget)} & \href{../syntax/components.html#syntax-aliastarget}{\mathit{aliastarget}} &::=&
\href{../syntax/components.html#syntax-aliastarget}{\mathsf{export}}~\href{../syntax/components.html#syntax-instanceidx}{\mathit{instanceidx}}~\href{../syntax/values.html#syntax-name}{\mathit{name}}\\&&|&
\href{../syntax/components.html#syntax-aliastarget}{\mathsf{core\_export}}~\href{../syntax/components.html#syntax-coreinstanceidx}{\mathit{core{:}instanceidx}}~\href{../syntax/values.html#syntax-name}{\mathit{name}}\\&&|&
\href{../syntax/components.html#syntax-aliastarget}{\mathsf{outer}}~\href{../syntax/values.html#syntax-int}{\mathit{u32}}~\href{../syntax/values.html#syntax-int}{\mathit{u32}}\\
\end{array}\end{split}\]
Canonical definitions¶
Canonical definitions are the only way to convert between Core WebAssembly functions and component-level shared-nothing functions which produce and consume values of type \(valtype\). A canon lift definition converts a core WebAssembly function into a component-level function which may be exported or used to satisfy the imports of another component; a canon lower definition converts an lifted function (often imported) into a core function.
\[\begin{split}\begin{array}{llcl}
\def\mathdef2256#1{{}}\mathdef2256{(canon)} & \href{../syntax/components.html#syntax-canon}{\mathit{canon}} &::=&
\href{../syntax/components.html#syntax-canon}{\mathsf{lift}}~\href{https://webassembly.github.io/spec/core/syntax/modules.html#syntax-funcidx}{\mathit{core{:}}\mathit{funcidx}}~\href{../syntax/components.html#syntax-canonopt}{\mathit{canonopt}}^{*}~\href{../syntax/components.html#syntax-typeidx}{\mathit{typeidx}}\\&&|&
\href{../syntax/components.html#syntax-canon}{\mathsf{lower}}~\href{../syntax/components.html#syntax-funcidx}{\mathit{funcidx}}~\href{../syntax/components.html#syntax-canonopt}{\mathit{canonopt}}^{*}\\
\def\mathdef2256#1{{}}\mathdef2256{(canonopt)} & \href{../syntax/components.html#syntax-canonopt}{\mathit{canonopt}} &::=&
\href{../syntax/components.html#syntax-canonopt}{\mathsf{string\_encoding\_utf8}}\\&&|&
\href{../syntax/components.html#syntax-canonopt}{\mathsf{string\_encoding\_utf16}}\\&&|&
\href{../syntax/components.html#syntax-canonopt}{\mathsf{string\_encoding\_latin1{+}utf16}}\\&&|&
\href{../syntax/components.html#syntax-canonopt}{\mathsf{memory}}~\href{https://webassembly.github.io/spec/core/syntax/modules.html#syntax-memidx}{\mathit{core{:}}\mathit{memidx}}\\&&|&
\href{../syntax/components.html#syntax-canonopt}{\mathsf{realloc}}~\href{https://webassembly.github.io/spec/core/syntax/modules.html#syntax-funcidx}{\mathit{core{:}}\mathit{funcidx}}\\&&|&
\href{../syntax/components.html#syntax-canonopt}{\mathsf{post\_return}}~\href{https://webassembly.github.io/spec/core/syntax/modules.html#syntax-funcidx}{\mathit{core{:}}\mathit{funcidx}}\\
\end{array}\end{split}\]
Start definitions¶
A start definition specifies a component function which this component would like to see called at instantiation type in order to do some sort of initialization.
\[\begin{array}{llcl}
\def\mathdef2256#1{{}}\mathdef2256{(start)} & \href{../syntax/components.html#syntax-start}{\mathit{start}} &::=& \{ \href{../syntax/components.html#syntax-start}{\mathsf{func}}~\href{../syntax/components.html#syntax-funcidx}{\mathit{funcidx}}, \href{../syntax/components.html#syntax-start}{\mathsf{args}}~\href{../syntax/components.html#syntax-valueidx}{\mathit{valueidx}}^{*} \}
\end{array}\]
Imports¶
Since an imported value is described entirely by its type, an actual import definition is effectively the same thing as an import declaration:
\[\begin{array}{llcl}
\def\mathdef2256#1{{}}\mathdef2256{(import)} & \href{../syntax/components.html#syntax-import}{\mathit{import}} &::=& \href{../syntax/types.html#syntax-importdecl}{\mathit{importdecl}}
\end{array}\]
Exports¶
An export definition is simply a name and a reference to another definition to export:
\[\begin{array}{llll}
\def\mathdef2256#1{{}}\mathdef2256{(export)} & \href{../syntax/components.html#syntax-export}{\mathit{export}} &::=& \{ \href{../syntax/components.html#syntax-export}{\mathsf{name}}~\href{../syntax/values.html#syntax-name}{\mathit{name}}, \href{../syntax/components.html#syntax-export}{\mathsf{def}}~\href{../syntax/components.html#syntax-sortidx}{\mathit{sortidx}} \}
\end{array}\]