Add NoDiscard attributes

psalm.xml

@@ -16,5 +16,6 @@
     </projectFiles>
     <issueHandlers>
         <InvalidOperand errorLevel="suppress" />
+        <UndefinedAttributeClass errorLevel="suppress" />
     </issueHandlers>
 </psalm>

src/Alpha.php

@@ -24,6 +24,7 @@ private function __construct(float $value)
     /**
      * @psalm-pure
      */
+    #[\NoDiscard]
     public static function max(): self
     {
         return new self(1);
@@ -34,6 +35,7 @@ public static function max(): self
      *
      * @return Attempt<self>
      */
+    #[\NoDiscard]
     public static function of(float $value): Attempt
     {
         return Attempt::of(static fn() => new self($value));
@@ -44,6 +46,7 @@ public static function of(float $value): Attempt
      *
      * @return Attempt<self>
      */
+    #[\NoDiscard]
     public static function fromHexadecimal(string $hex): Attempt
     {
         if (\mb_strlen($hex) === 1) {
@@ -53,6 +56,7 @@ public static function fromHexadecimal(string $hex): Attempt
         return self::of(\round(\hexdec($hex) / 255, 2));
     }
 
+    #[\NoDiscard]
     public function add(self $alpha): self
     {
         return new self(
@@ -63,6 +67,7 @@ public function add(self $alpha): self
         );
     }
 
+    #[\NoDiscard]
     public function subtract(self $alpha): self
     {
         return new self(
@@ -73,26 +78,31 @@ public function subtract(self $alpha): self
         );
     }
 
+    #[\NoDiscard]
     public function equals(self $alpha): bool
     {
         return $this->value === $alpha->toFloat();
     }
 
+    #[\NoDiscard]
     public function atMaximum(): bool
     {
         return $this->value === 1.0;
     }
 
+    #[\NoDiscard]
     public function atMinimum(): bool
     {
         return $this->value === 0.0;
     }
 
+    #[\NoDiscard]
     public function toFloat(): float
     {
         return $this->value;
     }
 
+    #[\NoDiscard]
     public function toHexadecimal(): string
     {
         return \str_pad(
@@ -105,6 +115,7 @@ public function toHexadecimal(): string
         );
     }
 
+    #[\NoDiscard]
     public function toString(): string
     {
         return (string) $this->value;

src/Black.php

@@ -23,6 +23,7 @@ private function __construct(
      *
      * @param int<0, 100> $value
      */
+    #[\NoDiscard]
     public static function at(int $value): self
     {
         return new self($value);
@@ -33,6 +34,7 @@ public static function at(int $value): self
      *
      * @return Attempt<self>
      */
+    #[\NoDiscard]
     public static function of(int $value): Attempt
     {
         if ($value < 0 || $value > 100) {
@@ -42,6 +44,7 @@ public static function of(int $value): Attempt
         return Attempt::result(new self($value));
     }
 
+    #[\NoDiscard]
     public function add(self $black): self
     {
         return new self(
@@ -52,6 +55,7 @@ public function add(self $black): self
         );
     }
 
+    #[\NoDiscard]
     public function subtract(self $black): self
     {
         return new self(
@@ -62,16 +66,19 @@ public function subtract(self $black): self
         );
     }
 
+    #[\NoDiscard]
     public function equals(self $black): bool
     {
         return $this->value === $black->toInt();
     }
 
+    #[\NoDiscard]
     public function atMaximum(): bool
     {
         return $this->value === 100;
     }
 
+    #[\NoDiscard]
     public function atMinimum(): bool
     {
         return $this->value === 0;
@@ -80,11 +87,13 @@ public function atMinimum(): bool
     /**
      * @return int<0, 100>
      */
+    #[\NoDiscard]
     public function toInt(): int
     {
         return $this->value;
     }
 
+    #[\NoDiscard]
     public function toString(): string
     {
         return (string) $this->value;

src/Blue.php

@@ -23,6 +23,7 @@ private function __construct(
      *
      * @param int<0, 255> $value
      */
+    #[\NoDiscard]
     public static function at(int $value): self
     {
         return new self($value);
@@ -33,6 +34,7 @@ public static function at(int $value): self
      *
      * @return Attempt<self>
      */
+    #[\NoDiscard]
     public static function of(int $value): Attempt
     {
         if ($value < 0 || $value > 255) {
@@ -47,6 +49,7 @@ public static function of(int $value): Attempt
      *
      * @return Attempt<self>
      */
+    #[\NoDiscard]
     public static function fromHexadecimal(string $hex): Attempt
     {
         if (\mb_strlen($hex) === 1) {
@@ -59,13 +62,15 @@ public static function fromHexadecimal(string $hex): Attempt
     /**
      * @return Attempt<self>
      */
+    #[\NoDiscard]
     public static function fromIntensity(Intensity $intensity): Attempt
     {
         return self::of(
             (int) \round((255 * $intensity->toInt()) / 100),
         );
     }
 
+    #[\NoDiscard]
     public function add(self $blue): self
     {
         return new self(
@@ -76,6 +81,7 @@ public function add(self $blue): self
         );
     }
 
+    #[\NoDiscard]
     public function subtract(self $blue): self
     {
         return new self(
@@ -86,16 +92,19 @@ public function subtract(self $blue): self
         );
     }
 
+    #[\NoDiscard]
     public function equals(self $blue): bool
     {
         return $this->integer === $blue->toInt();
     }
 
+    #[\NoDiscard]
     public function atMaximum(): bool
     {
         return $this->integer === 255;
     }
 
+    #[\NoDiscard]
     public function atMinimum(): bool
     {
         return $this->integer === 0;
@@ -104,11 +113,13 @@ public function atMinimum(): bool
     /**
      * @return int<0, 255>
      */
+    #[\NoDiscard]
     public function toInt(): int
     {
         return $this->integer;
     }
 
+    #[\NoDiscard]
     public function toString(): string
     {
         return \str_pad(