This crate provides a minimal fallback for the standard library’s allocator API, which is currently unstable.
Because allocator-fallback can be configured to re-export the real
unstable allocator API (see Crate features), users
of this crate must make sure they conditionally enable
#![feature(allocator_api)] in preparation for this occurrence; otherwise,
compilation errors may occur. This is the case even for crates that never
directly enable allocator-fallback’s allocator_api feature, because a
different crate that also depends on allocator-fallback could enable it.
To accomplish this, in Cargo.toml, duplicate your dependency on
allocator-fallback in the [build-dependencies] section. For example:
```toml [dependencies] allocator-fallback = "0.1.7"
[build-dependencies] allocator-fallback = "0.1.7" ```
Then, add a build script (build.rs) with the following
contents:[^1]
rust
fn main() {
if allocator_fallback::HAS_ALLOCATOR_API {
println!("cargo:rustc-cfg=has_allocator_api");
}
println!("cargo:rerun-if-changed=build.rs");
}
Finally, at the top of your crate root (likely lib.rs or main.rs), add
the following:
```rust
```
The instructions above will not work if allocator-fallback is declared
as an optional dependency. In this case, adjust the instructions as
follows:
Duplicate the dependency on allocator-fallback in [build-dependencies]
as before, keeping optional = true in both occurrences. For example:
```toml [dependencies.allocator-fallback] version = "0.1.7" optional = true
[build-dependencies.allocator-fallback] version = "0.1.7" optional = true ```
Then, use the following as the contents of your build script (build.rs)
instead:[^1]
rust
fn main() {
#[cfg(feature = "allocator-fallback")]
if allocator_fallback::HAS_ALLOCATOR_API {
println!("cargo:rustc-cfg=has_allocator_api");
}
println!("cargo:rerun-if-changed=build.rs");
}
Finally, as before, add the following to the top of your crate root:
```rust
```
domain using the [CC0 1.0 Universal Public Domain Dedication][CC0].
If the crate feature allocator_api is enabled, this crate will simply
re-export the real allocator API in the standard library. Of course, this
requires Rust nightly.
If the crate feature std is enabled (the default), the crate will use
[std]; otherwise, it will be no_std. Using [std] allows
[AllocError] to implement [std::error::Error].