144 lines
3.7 KiB
Markdown
144 lines
3.7 KiB
Markdown
# Instant
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If you call `std::time::Instant::now()` on a WASM platform, it will panic. This crate provides a partial
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replacement for `std::time::Instant` that works on WASM too. This defines the type `instant::Instant` which is:
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* A struct emulating the behavior of **std::time::Instant** if you are targeting `wasm32-unknown-unknown` or `wasm32-unknown-asmjs`
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**and** you enabled either the `stdweb` or the `wasm-bindgen` feature. This emulation is based on the javascript `performance.now()` function.
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* A type alias for `std::time::Instant` otherwise.
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Note that even if the **stdweb** or **wasm-bindgen** feature is enabled, this crate will continue to rely on `std::time::Instant`
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as long as you are not targeting wasm32. This allows for portable code that will work on both native and WASM platforms.
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This crate also exports the function `instant::now()` which returns a representation of the current time as an `f64`, expressed in milliseconds, in a platform-agnostic way. `instant::now()` will either:
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* Call `performance.now()` when compiling for a WASM platform with the features **stdweb** or **wasm-bindgen** enabled, or using a custom javascript function.
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* Return the time elapsed since the *Unix Epoch* on *native*, *non-WASM* platforms.
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*Note*: The old feature, `now`, has been deprecated. `instant::now()` is always exported and the `now` feature flag no longer has any effect. It remains listed in `Cargo.toml` to avoid introducing breaking changes and may be removed in future versions.
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## Examples
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### Using `instant` for a native platform.
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_Cargo.toml_:
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```toml
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[dependencies]
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instant = "0.1"
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```
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_main.rs_:
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```rust
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fn main() {
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// Will be the same as `std::time::Instant`.
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let now = instant::Instant::now();
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}
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```
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-----
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### Using `instant` for a WASM platform.
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This example shows the use of the `stdweb` feature. It would be similar with `wasm-bindgen`.
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_Cargo.toml_:
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```toml
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[dependencies]
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instant = { version = "0.1", features = [ "stdweb" ] }
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```
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_main.rs_:
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```rust
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fn main() {
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// Will emulate `std::time::Instant` based on `performance.now()`.
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let now = instant::Instant::now();
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}
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```
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-----
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### Using `instant` for a WASM platform where `performance.now()` is not available.
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This example shows the use of the `inaccurate` feature.
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_Cargo.toml_:
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```toml
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[dependencies]
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instant = { version = "0.1", features = [ "wasm-bindgen", "inaccurate" ] }
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```
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_main.rs_:
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```rust
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fn main() {
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// Will emulate `std::time::Instant` based on `Date.now()`.
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let now = instant::Instant::now();
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}
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```
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-----
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### Using `instant` for any platform enabling a feature transitively.
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_Cargo.toml_:
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```toml
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[features]
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stdweb = [ "instant/stdweb" ]
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wasm-bindgen = [ "instant/wasm-bindgen" ]
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[dependencies]
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instant = "0.1"
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```
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_lib.rs_:
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```rust
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fn my_function() {
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// Will select the proper implementation depending on the
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// feature selected by the user.
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let now = instant::Instant::now();
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}
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```
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-----
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### Using `instant::now()`
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_Cargo.toml_:
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```toml
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[features]
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stdweb = [ "instant/stdweb" ]
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wasm-bindgen = [ "instant/wasm-bindgen" ]
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[dependencies]
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instant = "0.1"
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```
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_lib.rs_:
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```rust
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fn my_function() {
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// Will select the proper implementation depending on the
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// feature selected by the user.
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let now_instant = instant::Instant::now();
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let now_milliseconds = instant::now(); // In milliseconds.
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}
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```
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### Using the feature `now` without `stdweb` or `wasm-bindgen`.
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_Cargo.toml_:
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```toml
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[dependencies]
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instant = "0.1"
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```
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_lib.rs_:
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```rust
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fn my_function() {
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// Will use the 'now' javascript implementation.
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let now_instant = instant::Instant::now();
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let now_milliseconds = instant::now(); // In milliseconds.
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}
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```
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_javascript WASM bindings file_:
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```js
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function now() {
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return Date.now() / 1000.0;
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}
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```
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