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<div class="sourceCode"><pre class="sourceCode rust"><code class="sourceCode rust"><span class="kw">static</span> S_2_0: [<span class="dt">usize</span>; <span class="dv">2</span>] = [<span class="dv">2</span>, <span class="dv">0</span>];
<span class="kw">pub</span> <span class="kw">fn</span> main() {
<span class="kw">let</span> s_1_0_2 = [<span class="dv">1</span>, <span class="dv">0</span>, <span class="dv">2</span>];
<span class="kw">let</span> first_choice: &[<span class="dt">usize</span>] = choose(&s_1_0_2, &S_2_0);
<span class="pp">println!</span>(<span class="st">"first_choice: {:?}"</span>, first_choice);
<span class="kw">let</span> second_choice = subdata_then_choose();
<span class="pp">println!</span>(<span class="st">"second_choice: {:?}"</span>, second_choice);
}
<span class="co">// EXERCISE 1: In `fn choose`, remove the `<'a>` and all occurrences</span>
<span class="co">// of `'a` from the signature of `fn choose`. What happens? Why?</span>
<span class="kw">fn</span> choose<<span class="ot">'a</span>>(x: &<span class="ot">'a</span> [<span class="dt">usize</span>], y: &<span class="ot">'a</span> [<span class="dt">usize</span>]) -> &<span class="ot">'a</span> [<span class="dt">usize</span>] {
<span class="co">// A semi-arbitrary predicate between the two inputs</span>
<span class="kw">if</span> y[x[<span class="dv">0</span>]] > x[y[<span class="dv">0</span>]] {
x
} <span class="kw">else</span> {
y
}
}
<span class="co">// EXERCISE 2: In `fn subdata_then_choose`, remove `return &ARRAY;`</span>
<span class="co">// (marked `XXX`) and uncomment alternative code there. What happens</span>
<span class="co">// when you try to compile this? What are some ways to address this?</span>
<span class="kw">fn</span> subdata_then_choose<<span class="ot">'a</span>>() -> &<span class="ot">'a</span> [<span class="dt">usize</span>] {
<span class="kw">return</span> &ARRAY; <span class="co">// XXX</span>
<span class="co">/*</span>
<span class="co"> let s_1_0_0 = [1, 0, 0];</span>
<span class="co"> let s_0_2_0 = [0, 2, 0];</span>
<span class="co"> choose(&s_1_0_0, &s_0_2_0)</span>
<span class="co"> */</span>
}
<span class="kw">static</span> ARRAY : [<span class="dt">usize</span>; <span class="dv">3</span>] = [<span class="dv">0</span>,<span class="dv">1</span>,<span class="dv">2</span>];
<span class="kw">const</span> C_2_0: [<span class="dt">usize</span>; <span class="dv">2</span>] = [<span class="dv">2</span>, <span class="dv">0</span>];
<span class="co">// (EXTRA CREDIT)</span>
<span class="co">// EXERCISE 3: In `fn main`, replace `&S_2_0` with `&C_2_0`.</span>
<span class="co">//</span>
<span class="co">// * Investigate: why does the code stop compiling?</span>
<span class="co">//</span>
<span class="co">// * How could we address this (within the body of `fn main` alone)?</span>
<span class="co">//</span>
<span class="co">// * Why did the original code with `S_2_0` compile?</span></code></pre></div>
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