prove how to safely validate precision

assert.php

<?php

set_error_handler(function($severity, $message, $filename, $lineno) {
    throw new \Error($message, $severity);
});

function strictAssert($expected, $actual) {
    if ($actual !== $expected) {
        echo PHP_EOL . '✋' . PHP_EOL;
        var_dump($actual, $expected);
        die;
    }
}

function because(string $proposition, callable $test) {
    echo "$proposition";

    try {
        $test();
    } catch (\Throwable $e) {
        echo PHP_EOL . $e->getMessage() . PHP_EOL;
        die;
    }

    echo " 👍" . PHP_EOL;
}

echo 'Becasue …' . PHP_EOL;

because("commas in strings ruin float conversion", function() {
    strictAssert( (float) '2000.45', 2000.45 );
    strictAssert( (float) '2,000.45', 2.0 );
});

because("weird types and values will actually coerce", function() {
    strictAssert( (float) '', 0.0 );
    strictAssert( (float) '2,000.45', 2.0 );
});

because("floats compact leading and trailing zeros", function() {
    strictAssert( (string) 1.100, '1.1' );
    strictAssert( (string) 00.35, '0.35' );
});

because("number_format coerces to float and will warn about some confusing values/types", function() {
    // number_format considers bool|null to be safely coercible, though I find this to be an odd excecption

    strictAssert( number_format(null, 2), '0.00' );
    strictAssert( number_format(false, 2), '0.00' );
    strictAssert( number_format(true, 2), '1.00' );

    // number_format warns about ambigous values

    try {
        $result = number_format('');
    } catch (\Throwable $e) {
        strictAssert($e->getmessage(), 'number_format() expects parameter 1 to be float, string given');
    }

    // note: warnings won't evaluate to a result
    // also-note: typically warnings won't halt execution (tricky)
    strictAssert(!isset($result), true);

    try {
        number_format('2,000.45');
    } catch (\Throwable $e) {
        strictAssert($e->getmessage(), 'A non well formed numeric value encountered');
    }

    try {
        number_format([0,1,2]);
    } catch (\Throwable $e) {
        strictAssert($e->getmessage(), 'number_format() expects parameter 1 to be float, array given');
    }
});

because("number_format will round based on precision", function() {
    strictAssert( number_format(0.2349, 2), '0.23' );
    strictAssert( number_format(0.235, 2), '0.24' );
});

because("number_format will add commas", function() {
    strictAssert( number_format(999, 2), '999.00' );
    strictAssert( number_format(1000, 2), '1,000.00' );
});