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When teaching the course, I got a little tripped up thinking students would need to make the `VerbosityFilter` generic over `Logger`. Let's be clearer that this is not required, and will be described later. This also updates the generic-types slide to repeat the exercise, completing that thought.
52 lines
1.4 KiB
Rust
52 lines
1.4 KiB
Rust
// Copyright 2024 Google LLC
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// ANCHOR: solution
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// ANCHOR: setup
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pub trait Logger {
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/// Log a message at the given verbosity level.
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fn log(&self, verbosity: u8, message: &str);
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}
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struct StderrLogger;
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impl Logger for StderrLogger {
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fn log(&self, verbosity: u8, message: &str) {
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eprintln!("verbosity={verbosity}: {message}");
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}
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}
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/// Only log messages up to the given verbosity level.
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struct VerbosityFilter {
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max_verbosity: u8,
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inner: StderrLogger,
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}
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// ANCHOR_END: setup
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impl Logger for VerbosityFilter {
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fn log(&self, verbosity: u8, message: &str) {
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if verbosity <= self.max_verbosity {
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self.inner.log(verbosity, message);
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}
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}
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}
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// ANCHOR: main
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fn main() {
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let logger = VerbosityFilter { max_verbosity: 3, inner: StderrLogger };
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logger.log(5, "FYI");
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logger.log(2, "Uhoh");
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}
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// ANCHOR_END: main
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