Derives [GetSize] for structs and enums.
The derive macro will provide a costum implementation of the [get_heap_size] method, which will simply call [get_heap_size] on all contained values and add the values up. This implies that by default all values contained in the struct or enum most implement the [GetSize] trait themselves.
Note that the derive macro does not support unions. You have to manually implement it for them.
Deriving [GetSize] for a struct:
```rust use get_size::GetSize;
pub struct OwnStruct { value1: String, value2: u64, }
fn main() { let test = OwnStruct { value1: "Hello".into(), value2: 123, };
assert_eq!(test.get_heap_size(), 5);
} ```
Deriving [GetSize] for an enum:
```rust use get_size::GetSize;
pub enum TestEnum { Variant1(u8, u16, u32), Variant2(String), Variant3, Variant4{x: String, y: String}, }
pub enum TestEnumNumber { Zero = 0, One = 1, Two = 2, }
fn main() { let test = TestEnum::Variant1(1, 2, 3); asserteq!(test.getheap_size(), 0);
let test = TestEnum::Variant2("Hello".into());
assert_eq!(test.get_heap_size(), 5);
let test = TestEnum::Variant3;
assert_eq!(test.get_heap_size(), 0);
let test = TestEnum::Variant4{x: "Hello".into(), y: "world".into()};
assert_eq!(test.get_heap_size(), 5 + 5);
let test = TestEnumNumber::One;
assert_eq!(test.get_heap_size(), 0);
} ```
The derive macro does also work with generics. The generated trait implementation will by default require all generic types to implement [GetSize] themselves, but this can be changed.
```rust use get_size::GetSize;
struct TestStructGenerics
enum TestEnumGenerics
fn main() {
let test: TestStructGenerics
assert_eq!(test.get_heap_size(), 5);
let test = String::from("Hello");
let test: TestEnumGenerics<String, u64> = TestEnumGenerics::Variant1(test);
assert_eq!(test.get_heap_size(), 5);
let test: TestEnumGenerics<String, u64> = TestEnumGenerics::Variant2(100);
assert_eq!(test.get_heap_size(), 0);
} ```
Deriving [GetSize] is straight forward if all the types contained in your data structure implement [GetSize] themselves, but this might not always be the case. For that reason the derive macro offers some helpers to assist you in that case.
Note that the helpers are currently only available for regular structs, that is they do neither support tuple structs nor enums.
You can tell the derive macro to ignore certain struct fields by adding the ignore attribute to them. The generated implementation of [get_heap_size] will then simple skip this field.
The idiomatic use case for this helper is if you use shared ownership and do not want your data to be counted twice.
```rust use std::sync::Arc; use get_size::GetSize;
struct PrimaryStore {
id: u64,
shared_data: Arc
struct SecondaryStore {
id: u64,
#[getsize(ignore)]
shareddata: Arc
fn main() { let shareddata = Arc::new(Vec::withcapacity(1024));
let primarydata = PrimaryStore { id: 1, shareddata: Arc::clone(&shared_data), };
let secondarydata = SecondaryStore { id: 2, shareddata, };
// Note that Arc does also store the Vec's stack data on the heap.
asserteq!(primarydata.getheapsize(), Vec::
But you may also use this as a band aid, if a certain struct fields type does not implement [GetSize].
Be aware though that this will result in an implementation which will return incorrect results, unless the heap size of that type is indeed always zero and can thus be ignored. It is therefor advisable to use one of the next two helper options instead.
```rust use get_size::GetSize;
// Does not implement GetSize! struct TestStructNoGetSize { value: String, }
// Implements GetSize, even through one field's type does not implement it.
struct TestStruct { name: String, #[getsize(ignore)] ignoredvalue: TestStructNoGetSize, }
fn main() { let ignored_value = TestStructNoGetSize { value: "Hello world!".into(), };
let test = TestStruct { name: "Adam".into(), ignored_value, };
// Note that the result is lower then it should be. asserteq!(test.getheap_size(), 4); } ```
In same cases you may be dealing with external types which allocate a fixed amount of bytes at the heap. In this case you may use the size attribute to always account the given field with a fixed value.
```rust use get_size::GetSize;
struct TestStruct { id: u64, #[get_size(size = 1024)] buffer: Buffer1024, // Always allocates exactly 1KB at the heap. }
fn main() { let test = TestStruct { id: 1, buffer: Buffer1024::new(), };
asserteq!(test.getheap_size(), 1024); } ```
In same cases you may be dealing with an external data structure for which you know how to calculate its heap size using its public methods. In that case you may either use the newtype pattern to implement [GetSize] for it directly, or you can use the size_fn attribute, which will call the given function in order to calculate the fields heap size.
The latter is especially usefull if you can make use of a certain trait to calculate the heap size for multiple types.
Note that unlike in other crates, the name of the function to be called is not encapsulated by double-quotes ("), but rather given directly.
```rust use get_size::GetSize;
struct TestStruct {
id: u64,
#[getsize(sizefn = vecalikehelper)]
buffer: ExternalVecAlike
// NOTE: We assume that slice.len()==slice.capacity()
fn vecalikehelper
fn main() {
let buffer = vec![0u8; 512];
let buffer: ExternalVecAlike
let test = TestStruct { id: 1, buffer, };
asserteq!(test.getheap_size(), 512); } ```
If your struct uses generics, but the fields at which they are stored are ignored or get handled by helpers because the generic does not implement [GetSize], you will have to mark these generics with a special struct level ignore attribute. Otherwise the derived [GetSize] implementation would still require these generics to implement [GetSize], even through there is no need for it.
```rust use get_size::GetSize;
struct TestStructHelpers
// Does not implement GetSize struct NoGS {}
fn getsizehelper
fn main() {
let test: TestStructHelpers
assert_eq!(test.get_heap_size(), 5 + 100 + 50);
} ```
The derive macro will panic if used on unions since these are currently not supported.
Note that there will be a compilation error if one of the (not ignored) values encountered does not implement the [GetSize] trait.
This library is licensed under the MIT license.
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in this library by you, shall be licensed as MIT, without any additional terms or conditions.