Initial import of Instant crate

Version 0.1.7

Bug: 169931010
Test: build
Change-Id: I12dd69b9b9ee5217d3ac5499cdc353b297d13e92

1 files changed, 124 insertions, 0 deletions

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+# Instant
+
+If you call `std::time::Instant::now()` on a WASM platform, it will panic. This crate provides a partial
+replacement for `std::time::Instant` that works on WASM too. This defines the type `instant::Instant` which is:
+
+* A struct emulating the behavior of **std::time::Instant** if you are targeting `wasm32-unknown-unknown` or `wasm32-unknown-asmjs`
+**and** you enabled either the `stdweb` or the `wasm-bindgen` feature. This emulation is based on the javascript `performance.now()` function.
+* A type alias for `std::time::Instant` otherwise.
+
+
+
+Note that even if the **stdweb** or **wasm-bindgen** feature is enabled, this crate will continue to rely on `std::time::Instant`
+as long as you are not targeting wasm32. This allows for portable code that will work on both native and WASM platforms.
+
+### The feature `now`.
+By enabling the feature `now` the function `instant::now()` will be exported and will either:
+
+* Call `performance.now()` when compiling for a WASM platform with the features **stdweb** or **wasm-bindgen** enabled, or using a custom javascript function.
+* Call `time::precise_time_s() * 1000.0` otherwise.
+
+The result is expressed in milliseconds.
+
+## Examples
+### Using `instant` for a native platform.
+_Cargo.toml_:
+```toml
+[dependencies]
+instant = "0.1"
+```
+
+_main.rs_:
+```rust
+fn main() {
+    // Will be the same as `std::time::Instant`.
+    let now = instant::Instant::new();
+}
+```
+
+-----
+
+### Using `instant` for a WASM platform.
+This example shows the use of the `stdweb` feature. It would be similar with `wasm-bindgen`.
+
+_Cargo.toml_:
+```toml
+[dependencies]
+instant = { version = "0.1", features = [ "stdweb" ] }
+```
+
+_main.rs_:
+```rust
+fn main() {
+    // Will emulate `std::time::Instant` based on `performance.now()`.
+    let now = instant::Instant::new();
+}
+```
+
+-----
+
+### Using `instant` for any platform enabling a feature transitively.
+_Cargo.toml_:
+```toml
+[features]
+stdweb = [ "instant/stdweb" ]
+wasm-bindgen = [ "instant/wasm-bindgen" ]
+
+[dependencies]
+instant = "0.1"
+```
+
+_lib.rs_:
+```rust
+fn my_function() {
+    // Will select the proper implementation depending on the
+    // feature selected by the user.
+    let now = instant::Instant::new();
+}
+```
+
+-----
+
+### Using the feature `now`.
+_Cargo.toml_:
+```toml
+[features]
+stdweb = [ "instant/stdweb" ]
+wasm-bindgen = [ "instant/wasm-bindgen" ]
+
+[dependencies]
+instant = { version = "0.1", features = [ "now" ] }
+```
+
+_lib.rs_:
+```rust
+fn my_function() {
+    // Will select the proper implementation depending on the
+    // feature selected by the user.
+    let now_instant = instant::Instant::new();
+    let now_milliseconds = instant::now(); // In milliseconds.
+}
+```
+
+### Using the feature `now` without `stdweb` or `wasm-bindgen`.
+_Cargo.toml_:
+```toml
+[dependencies]
+instant = { version = "0.", features = [ "now" ] }
+```
+
+_lib.rs_:
+```rust
+fn my_function() {
+    // Will use the 'now' javascript implementation.
+    let now_instant = instant::Instant::new();
+    let now_milliseconds = instant::now(); // In milliseconds.
+}
+```
+
+_javascript WASM bindings file_:
+```js
+function now() {
+	return Date.now() / 1000.0;
+}
+```