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# graphannis-malloc_size_of_derive

This is a fork of the `malloc_size_of_derive` crate, which is part of the [Servo codebase](https://github.com/servo/servo/tree/master/components/malloc_size_of_derive) but not published on crates.io yet. 
The intention of this fork is to make the functionality of the original crate available to the [graphANNIS](https://github.com/corpus-tools/graphANNIS) corpus search library, which is published on [crates.io](https://crates.io/crates/graphannis).

## `with_malloc_size_of_func` field attribute

In comparision to the original crate, a new `with_malloc_size_of_func` field attribute for structs was added to allow overriding the default calculation with a custom function.
E.g. you can write
```rust
fn custom_func(obj: &Bar, ops: &mut MallocSizeOfOps) -> usize {
    // do some custom calculations
}

#[derive(MallocSizeOf)]
struct Foo {
    bar: Baz,
    #[with_malloc_size_of_func = "custom_func"]
    baz: Bar,
}
```

This mechanism allows useful if `MallocSizeOf` can be derived normally for some fields but not for others.
Instead of implementing `MallocSizeOf` manually for the whole struct (where it is easy to forget some fields), only the missing information for the specific fields need to be provided.