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sp-runtime-interface add table about FFI types (#4668)

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Adds a table to the rustdoc that shows how each individual type is
passed between the wasm and the host side.
This commit is contained in:
Bastian Köcher
2020-01-18 13:51:12 +01:00
committed by Gavin Wood
parent b72ba98b97
commit 1b9baad04f
3 changed files with 34 additions and 7 deletions
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substrate/primitives/runtime-interface/src/lib.rs
+29 -1
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@@ -28,7 +28,7 @@
//! implement [`RIType`]. The associated type `FFIType` is the type that is used in the FFI
//! function to represent the actual type. For example `[T]` is represented by an `u64`. The slice
//! pointer and the length will be mapped to an `u64` value. For more information, see the
//! implementation of [`RIType`] for [`T`]. The FFI function definition is used when calling from
//! implementation of [`RIType`] for `T`. The FFI function definition is used when calling from
//! the wasm runtime into the node.
//!
//! Traits are used to convert from a type to the corresponding [`RIType::FFIType`].
@@ -69,6 +69,34 @@
//!
//! For more information on declaring a runtime interface, see
//! [`#[runtime_interface]`](attr.runtime_interface.html).
//!
//! # FFI type and conversion
//!
//! The following table documents how values of types are passed between the wasm and
//! the host side and how they are converted into the corresponding type.
//!
//! | Type | FFI type | Conversion |
//! |----|----|----|
//! | `u8` | `u8` | `Identity` |
//! | `u16` | `u16` | `Identity` |
//! | `u32` | `u32` | `Identity` |
//! | `u64` | `u64` | `Identity` |
//! | `i8` | `i8` | `Identity` |
//! | `i16` | `i16` | `Identity` |
//! | `i32` | `i32` | `Identity` |
//! | `i64` | `i64` | `Identity` |
//! | `bool` | `u8` | `if v { 1 } else { 0 }` |
//! | `&str` | `u64` | <code>v.len() 32bit << 32 &#124; v.as_ptr() 32bit</code> |
//! | `&[u8]` | `u64` | <code>v.len() 32bit << 32 &#124; v.as_ptr() 32bit</code> |
//! | `Vec<u8>` | `u64` | <code>v.len() 32bit << 32 &#124; v.as_ptr() 32bit</code> |
//! | `Vec<T> where T: Encode` | `u64` | `let e = v.encode();`<br><br><code>e.len() 32bit << 32 &#124; e.as_ptr() 32bit</code> |
//! | `&[T] where T: Encode` | `u64` | `let e = v.encode();`<br><br><code>e.len() 32bit << 32 &#124; e.as_ptr() 32bit</code> |
//! | `[u8; N]` | `u32` | `v.as_ptr()` |
//! | `*const T` | `u32` | `Identity` |
//! | [`T where T: PassBy<PassBy=Inner>`](pass_by::Inner) | Depends on inner | Depends on inner |
//! | [`T where T: PassBy<PassBy=Codec>`](pass_by::Codec) | `u64`| <code>v.len() 32bit << 32 &#124; v.as_ptr() 32bit</code> |
//!
//! `Identity` means that the value is converted directly into the corresponding FFI type.
#![cfg_attr(not(feature = "std"), no_std)]