Types¶
The component model introduces two new kinds of types: value types, which are used to classify shared-nothing interface values, and definition types, which are used to characterize the core and component modules, instances, and functions which form part of a a component’s interface.
Value types¶
A value type classifies a component-level abstract value. Unlike for Core WebAssembly values, no specified abstract syntax of component values exist; they serve simply to define the interface of lifted component functions (which currently may be produced only via canonical definitions).
Value types are further divided into primitive value types, which have a compact representation and can be found in most places where types are allowed, and defined value types, which must appear in a type definition before they can be used (via a \(\href{../syntax/components.html#syntax-typeidx}{\mathit{typeidx}}\) into the type index space):
\[\begin{split}\begin{array}{llcl}
\def\mathdef3609#1{{}}\mathdef3609{(primvaltype)} & \href{../syntax/types.html#syntax-primvaltype}{\mathit{primvaltype}} &::=&
\href{../syntax/types.html#syntax-valtype}{\mathsf{bool}}\\&&|&
\href{../syntax/types.html#syntax-valtype}{\mathsf{s8}} ~|~ \href{../syntax/types.html#syntax-valtype}{\mathsf{u8}} ~|~ \href{../syntax/types.html#syntax-valtype}{\mathsf{s16}} ~|~ \href{../syntax/types.html#syntax-valtype}{\mathsf{u16}} ~|~ \href{../syntax/types.html#syntax-valtype}{\mathsf{s32}} ~|~ \href{../syntax/types.html#syntax-valtype}{\mathsf{u32}} ~|~ \href{../syntax/types.html#syntax-valtype}{\mathsf{s64}} ~|~ \href{../syntax/types.html#syntax-valtype}{\mathsf{u64}}\\&&|&
\href{../syntax/types.html#syntax-valtype}{\mathsf{float32}} ~|~ \href{../syntax/types.html#syntax-valtype}{\mathsf{float64}}\\&&|&
\href{../syntax/types.html#syntax-valtype}{\mathsf{char}} ~|~ \href{../syntax/types.html#syntax-valtype}{\mathsf{string}}\\&&|&\\
\def\mathdef3609#1{{}}\mathdef3609{(defvaltype)} & \href{../syntax/types.html#syntax-defvaltype}{\mathit{defvaltype}} &::=&
\href{../syntax/types.html#syntax-valtype}{\mathsf{prim}}~\href{../syntax/types.html#syntax-primvaltype}{\mathit{primvaltype}}\\&&|&
\href{../syntax/types.html#syntax-valtype}{\mathsf{record}}~\href{../syntax/types.html#syntax-recordcase}{\mathit{record\_field}}^{+}\\&&|&
\href{../syntax/types.html#syntax-valtype}{\mathsf{variant}}~\href{../syntax/types.html#syntax-variantcase}{\mathit{variant\_case}}^{+}\\&&|&
\href{../syntax/types.html#syntax-valtype}{\mathsf{list}}~\href{../syntax/types.html#syntax-valtype}{\mathit{valtype}}\\&&|&
\href{../syntax/types.html#syntax-valtype}{\mathsf{tuple}}~\href{../syntax/types.html#syntax-valtype}{\mathit{valtype}}^{*}\\&&|&
\href{../syntax/types.html#syntax-valtype}{\mathsf{flags}}~\href{../syntax/values.html#syntax-name}{\mathit{name}}^{*}\\&&|&
\href{../syntax/types.html#syntax-valtype}{\mathsf{enum}}~\href{../syntax/values.html#syntax-name}{\mathit{name}}^{+}\\&&|&
\href{../syntax/types.html#syntax-valtype}{\mathsf{union}}~\href{../syntax/types.html#syntax-valtype}{\mathit{valtype}}^{+}\\&&|&
\href{../syntax/types.html#syntax-valtype}{\mathsf{option}}~\href{../syntax/types.html#syntax-valtype}{\mathit{valtype}}\\&&|&
\href{../syntax/types.html#syntax-valtype}{\mathsf{result}}~\href{../syntax/types.html#syntax-valtype}{\mathit{valtype}}^{?}~\href{../syntax/types.html#syntax-valtype}{\mathit{valtype}}^{?}\\&&|&
\href{../syntax/types.html#syntax-valtype}{\mathsf{own}}~\href{../syntax/components.html#syntax-typeidx}{\mathit{typeidx}}\\&&|&
\href{../syntax/types.html#syntax-valtype}{\mathsf{borrow}}~\href{../syntax/components.html#syntax-typeidx}{\mathit{typeidx}}\\
\def\mathdef3609#1{{}}\mathdef3609{(valtype)} &\href{../syntax/types.html#syntax-valtype}{\mathit{valtype}} &::=&
\href{../syntax/types.html#syntax-primvaltype}{\mathit{primvaltype}} ~|~ \href{../syntax/components.html#syntax-typeidx}{\mathit{typeidx}}
\end{array}\end{split}\]
\[\begin{split}\begin{array}{llll}
\def\mathdef3609#1{{}}\mathdef3609{(recordfield)} & \href{../syntax/types.html#syntax-recordcase}{\mathit{record\_field}} &::=&
\{ \href{../syntax/types.html#syntax-recordcase}{\mathsf{name}}~\href{../syntax/values.html#syntax-name}{\mathit{name}}, \href{../syntax/types.html#syntax-recordcase}{\mathsf{type}}~\href{../syntax/types.html#syntax-valtype}{\mathit{valtype}} \}\\
\def\mathdef3609#1{{}}\mathdef3609{(variantcase)} & \href{../syntax/types.html#syntax-variantcase}{\mathit{variant\_case}} &::=&
\{ \href{../syntax/types.html#syntax-variantcase}{\mathsf{name}}~\href{../syntax/values.html#syntax-name}{\mathit{name}}, \href{../syntax/types.html#syntax-variantcase}{\mathsf{type}}~\href{../syntax/types.html#syntax-valtype}{\mathit{valtype}}, \href{../syntax/types.html#syntax-variantcase}{\mathsf{refines}}~\href{../syntax/values.html#syntax-int}{\mathit{u32}}^? \}
\end{array}\end{split}\]
Resource types¶
\[\begin{array}{llll}
\def\mathdef3609#1{{}}\mathdef3609{(resourcetype)} & \href{../syntax/types.html#syntax-resourcetype}{\mathit{resourcetype}} &::= &
\{ \href{../syntax/types.html#syntax-resourcetype}{\mathsf{rep}}~\mathtt{i32}, \href{../syntax/types.html#syntax-resourcetype}{\mathsf{dtor}}~\href{../syntax/components.html#syntax-funcidx}{\mathit{funcidx}} \}
\end{array}\]
Function types¶
A component-level shared-nothing function is classified by the types of its parameters and return values. Such a function may take as parameters zero or more named values, and will return as results zero or more namde values. If a function takes a single parameter, or returns a single result, said parameter or result may be unnamed:
\[\begin{array}{llll}
\def\mathdef3609#1{{}}\mathdef3609{(functype)} & \href{../syntax/types.html#syntax-functype}{\mathit{functype}} &::=&
\href{../syntax/types.html#syntax-resulttype}{\mathit{resulttype}} \to \href{../syntax/types.html#syntax-resulttype}{\mathit{resulttype}}
\end{array}\]
The input or output of a function is classified by a result type:
\[\begin{split}\begin{array}{llcl}
\def\mathdef3609#1{{}}\mathdef3609{(resulttype)} & \href{../syntax/types.html#syntax-resulttype}{\mathit{resulttype}} &::=&
\href{../syntax/types.html#syntax-valtype}{\mathit{valtype}}\\&&|&
\{ \href{../syntax/types.html#syntax-resulttype}{\mathsf{name}}~\href{../syntax/values.html#syntax-name}{\mathit{name}}, \href{../syntax/types.html#syntax-resulttype}{\mathsf{type}}~\href{../syntax/types.html#syntax-valtype}{\mathit{valtype}} \}^{*}
\end{array}n\end{split}\]
Instance types¶
A component instance is conceptually classified by the types of its exports. However, an instance’s type is concretely represented as a series of declarations manipulating index spaces (particular to the instance type; these index spaces are entirely unrelated to both the index spaces of any instance which has this type and those of any instance importing or exporting something of this type). This allows for better type sharing and, in the future, uses of private types from parent components.
\[\begin{split}\begin{array}{llcl}
\def\mathdef3609#1{{}}\mathdef3609{(instancetype)} & \href{../syntax/types.html#syntax-instancetype}{\mathit{instancetype}} &::=& \href{../syntax/types.html#syntax-instancedecl}{\mathit{instancedecl}}^{*}\\
\def\mathdef3609#1{{}}\mathdef3609{(instancedecl)} & \href{../syntax/types.html#syntax-instancedecl}{\mathit{instancedecl}} &::=&
\href{../syntax/types.html#syntax-instancedecl}{\mathsf{alias}}~\href{../syntax/types.html#syntax-alias}{\mathit{alias}}\\&&|&
\href{../syntax/types.html#syntax-instancedecl}{\mathsf{core\_type}}~\href{https://webassembly.github.io/spec/core/syntax/types.html#syntax-functype}{\mathit{core{:}}\mathit{type}}\\&&|&
\href{../syntax/types.html#syntax-instancedecl}{\mathsf{type}}~\href{../syntax/types.html#syntax-deftype}{\mathit{deftype}}\\&&|&
\href{../syntax/types.html#syntax-instancedecl}{\mathsf{export}}~\href{../syntax/types.html#syntax-exportdecl}{\mathit{exportdecl}}\\
\def\mathdef3609#1{{}}\mathdef3609{(externdesc)} & \href{../syntax/types.html#syntax-externdesc}{\mathit{externdesc}} &::=&
\href{../syntax/types.html#syntax-externdesc}{\mathsf{type}}~\href{../syntax/types.html#syntax-typebound}{\mathit{typebound}}\\&&|&
\href{../syntax/types.html#syntax-externdesc}{\mathsf{core\_module}}~\href{https://webassembly.github.io/spec/core/syntax/modules.html#syntax-typeidx}{\mathit{core{:}}\mathit{typeidx}}\\&&|&
\href{../syntax/types.html#syntax-externdesc}{\mathsf{func}}~\href{../syntax/components.html#syntax-typeidx}{\mathit{typeidx}}\\&&|&
\href{../syntax/types.html#syntax-externdesc}{\mathsf{value}}~\href{../syntax/types.html#syntax-valtype}{\mathit{valtype}}\\&&|&
\href{../syntax/types.html#syntax-externdesc}{\mathsf{instance}}~\href{../syntax/components.html#syntax-typeidx}{\mathit{typeidx}}\\&&|&
\href{../syntax/types.html#syntax-externdesc}{\mathsf{component}}~\href{../syntax/components.html#syntax-typeidx}{\mathit{typeidx}}\\
\def\mathdef3609#1{{}}\mathdef3609{(typebound)} & \href{../syntax/types.html#syntax-typebound}{\mathit{typebound}} &::=&
\href{../syntax/types.html#syntax-typebound}{\mathsf{EQ}}~\href{../syntax/components.html#syntax-typeidx}{\mathit{typeidx}}\\&&|&
\href{../syntax/types.html#syntax-typebound}{\mathsf{SUB~resource}}\\&&|&
\dots\\
\def\mathdef3609#1{{}}\mathdef3609{(exportdecl)} & \href{../syntax/types.html#syntax-exportdecl}{\mathit{exportdecl}} &::=& \{ \href{../syntax/types.html#syntax-exportdecl}{\mathsf{name}}~\href{../syntax/values.html#syntax-name}{\mathit{name}}, \href{../syntax/types.html#syntax-exportdecl}{\mathsf{desc}}~\href{../syntax/types.html#syntax-externdesc}{\mathit{externdesc}} \}
\end{array}\end{split}\]
Component types¶
A component is conceptually classified by the types of its imports and exports. However, like instances, this is concretely represented as a series of declarations; in particular, a similar set of declarations allowing also for imports.
\[\begin{split}\begin{array}{llcl}
\def\mathdef3609#1{{}}\mathdef3609{(componenttype)} & \href{../syntax/types.html#syntax-componenttype}{\mathit{componenttype}} &::=& \href{../syntax/types.html#syntax-componentdecl}{\mathit{componentdecl}}^{*}\\
\def\mathdef3609#1{{}}\mathdef3609{(componentdecl)} & \href{../syntax/types.html#syntax-componentdecl}{\mathit{componentdecl}} &::=&
\href{../syntax/types.html#syntax-instancedecl}{\mathit{instancedecl}}\\&&|&
\href{../syntax/types.html#syntax-componentdecl}{\mathsf{import}}~\href{../syntax/types.html#syntax-importdecl}{\mathit{importdecl}}\\
\def\mathdef3609#1{{}}\mathdef3609{(importdecl)} & \href{../syntax/types.html#syntax-importdecl}{\mathit{importdecl}} &::=& \{ \href{../syntax/types.html#syntax-importdecl}{\mathsf{name}}~\href{../syntax/values.html#syntax-name}{\mathit{name}}, \href{../syntax/types.html#syntax-importdecl}{\mathsf{desc}}~\href{../syntax/types.html#syntax-externdesc}{\mathit{externdesc}} \}\\
\end{array}\end{split}\]
Definition types¶
A type definition may name a value, resource, function, component, or instance type:
\[\begin{split}\begin{array}{llcl}
\def\mathdef3609#1{{}}\mathdef3609{(deftype)} & \href{../syntax/types.html#syntax-deftype}{\mathit{deftype}} &::=&
\href{../syntax/types.html#syntax-defvaltype}{\mathit{defvaltype}}\\&&|&
\href{../syntax/types.html#syntax-resourcetype}{\mathit{resourcetype}}\\&&|&
\href{../syntax/types.html#syntax-functype}{\mathit{functype}}\\&&|&
\href{../syntax/types.html#syntax-componenttype}{\mathit{componenttype}}\\&&|&
\href{../syntax/types.html#syntax-instancetype}{\mathit{instancetype}}\\
\end{array}\end{split}\]
Core definition types¶
The component module specification also defines an expanded notion of what a core type is, which may eventually be subsumed by a core module linking extension.
\[\begin{split}\begin{array}{llcl}
\def\mathdef3609#1{{}}\mathdef3609{(coredeftype)} & \href{../syntax/types.html#syntax-coredeftype}{\mathit{core{:}deftype}} &::=&
\href{https://webassembly.github.io/spec/core/syntax/types.html#syntax-functype}{\mathit{core{:}}\mathit{functype}}\\&&|&
\href{../syntax/types.html#syntax-coremoduletype}{\mathit{core{:}moduletype}}\\
\def\mathdef3609#1{{}}\mathdef3609{(coremoduletype)} & \href{../syntax/types.html#syntax-coremoduletype}{\mathit{core{:}moduletype}} &::=& \href{../syntax/types.html#syntax-coremoduledecl}{\mathit{coremoduledecl}}^{*}\\
\def\mathdef3609#1{{}}\mathdef3609{(coremoduledecl)} & \href{../syntax/types.html#syntax-coremoduledecl}{\mathit{coremoduledecl}} &::=&
\href{../syntax/types.html#syntax-coreimportdecl}{\mathit{core{:}importdecl}}\\&&|&
\href{../syntax/types.html#syntax-coredeftype}{\mathit{core{:}deftype}}\\&&|&
\href{../syntax/types.html#syntax-corealias}{\mathit{core{:}alias}}\\&&|&
\href{../syntax/types.html#syntax-coreexportdecl}{\mathit{core{:}exportdecl}}\\
\def\mathdef3609#1{{}}\mathdef3609{(corealias)} & \href{../syntax/types.html#syntax-corealias}{\mathit{core{:}alias}} &::=& \{ \href{../syntax/types.html#syntax-corealias}{\mathsf{sort}}~\href{../syntax/components.html#syntax-coresort}{\mathit{core{:}sort}}, \href{../syntax/types.html#syntax-corealias}{\mathsf{target}}~\href{../syntax/types.html#syntax-corealiastarget}{\mathit{corealiastarget}} \}\\
\def\mathdef3609#1{{}}\mathdef3609{(corealiastarget)} & \href{../syntax/types.html#syntax-corealiastarget}{\mathit{corealiastarget}} &::=& \href{../syntax/types.html#syntax-corealiastarget}{\mathsf{outer}}~\href{../syntax/values.html#syntax-int}{\mathit{u32}}~\href{../syntax/values.html#syntax-int}{\mathit{u32}}\\
\def\mathdef3609#1{{}}\mathdef3609{(coreimportdecl)} & \href{../syntax/types.html#syntax-coreimportdecl}{\mathit{core{:}importdecl}} &::=& \href{https://webassembly.github.io/spec/core/syntax/modules.html#syntax-import}{\mathit{core{:}}\mathit{import}}\\
\def\mathdef3609#1{{}}\mathdef3609{(coreexportdecl)} & \href{../syntax/types.html#syntax-coreexportdecl}{\mathit{core{:}exportdecl}} &::=& \{ \href{../syntax/types.html#syntax-coreexportdecl}{\mathsf{name}}~\href{../syntax/values.html#syntax-name}{\mathit{name}}, \href{../syntax/types.html#syntax-coreexportdecl}{\mathsf{desc}}~\href{https://webassembly.github.io/spec/core/syntax/modules.html#syntax-importdesc}{\mathit{core{:}}\mathit{importdesc}} \}
\end{array}\end{split}\]