X-Git-Url: https://git.ladys.computer/Pisces/blobdiff_plain/37c295ffa9d5a062fe15d78427e2a7096a416bb3..50ab30fc3a257e46da6b8bdc0dad054f729e16e1:/value.js

diff --git a/value.js b/value.js
index 6471ea3..1039a3c 100644
--- a/value.js
+++ b/value.js
@@ -173,6 +173,343 @@ export const POSITIVE_ZERO = 0;
 /** The undefined primitive. */
 export const UNDEFINED = undefined;
 
+/**
+ * Completes the provided property descriptor by setting missing values
+ * to their defaults.
+ *
+ * ※ This method modifies the provided object and returns undefined.
+ */
+export const completePropertyDescriptor = (Desc) => {
+  if (Desc === UNDEFINED) {
+    throw new TypeError(
+      "Piscēs: Cannot complete undefined property descriptor.",
+    );
+  } else if (!("get" in Desc || "set" in Desc)) {
+    // This is a generic or data descriptor.
+    if (!("value" in Desc)) {
+      // `value` is not defined on this.
+      Desc.value = UNDEFINED;
+    } else {
+      // `value` is already defined on this.
+      /* do nothing */
+    }
+    if (!("writable" in Desc)) {
+      // `writable` is not defined on this.
+      Desc.writable = false;
+    } else {
+      // `writable` is already defined on this.
+      /* do nothing */
+    }
+  } else {
+    // This is not a generic or data descriptor.
+    if (!("get" in Desc)) {
+      // `get` is not defined on this.
+      Desc.get = UNDEFINED;
+    } else {
+      // `get` is already defined on this.
+      /* do nothing */
+    }
+    if (!("set" in Desc)) {
+      // `set` is not defined on this.
+      Desc.set = UNDEFINED;
+    } else {
+      // `set` is already defined on this.
+      /* do nothing */
+    }
+  }
+  if (!("enumerable" in Desc)) {
+    // `enumerable` is not defined on this.
+    Desc.enumerable = false;
+  } else {
+    // `enumerable` is already defined on this.
+    /* do nothing */
+  }
+  if (!("configurable" in Desc)) {
+    // `configurable` is not defined on this.
+    Desc.configurable = false;
+  } else {
+    // `configurable` is already defined on this.
+    /* do nothing */
+  }
+};
+
+/** Gets whether the provided value is an accessor descrtiptor. */
+export const isAccessorDescriptor = (Desc) =>
+  Desc !== UNDEFINED && ("get" in Desc || "set" in Desc);
+
+/** Gets whether the provided value is a data descrtiptor. */
+export const isDataDescriptor = (Desc) =>
+  Desc !== UNDEFINED && ("value" in Desc || "writable" in Desc);
+
+/**
+ * Gets whether the provided value is a fully‐populated property
+ * descriptor.
+ */
+export const isFullyPopulatedDescriptor = (Desc) =>
+  Desc !== UNDEFINED &&
+  ("value" in Desc && "writable" in Desc ||
+    "get" in Desc && "set" in Desc) &&
+  "enumerable" in Desc && "configurable" in Desc;
+
+/**
+ * Gets whether the provided value is a generic (not accessor or data)
+ * descrtiptor.
+ */
+export const isGenericDescriptor = (Desc) =>
+  Desc !== UNDEFINED &&
+  !("get" in Desc || "set" in Desc || "value" in Desc ||
+    "writable" in Desc);
+
+export const {
+  /**
+   * Returns whether the provided value is a property descriptor record
+   * as created by `toPropertyDescriptor`.
+   *
+   * ※ This function is provided to enable inspection of whether an
+   * object uses the property descriptor record proxy implementation,
+   * not as a general test of whether an object satisfies the
+   * requirements for property descriptors. In most cases, a more
+   * specific test, like `isAccessorDescriptor`, `isDataDescriptor`, or
+   * `isGenericDescriptor`, is preferrable.
+   */
+  isPropertyDescriptorRecord,
+
+  /**
+   * Converts the provided value to a property descriptor record.
+   *
+   * ※ The prototype of a property descriptor record is always `null`.
+   *
+   * ※ Actually constructing a property descriptor object using this
+   * class is only necessary if you need strict guarantees about the
+   * types of its properties; the resulting object is proxied to ensure
+   * the types match what one would expect from composing
+   * FromPropertyDescriptor and ToPropertyDescriptor in the Ecmascript
+   * specification.
+   */
+  toPropertyDescriptor,
+} = (() => {
+  const {
+    assign: setPropertyValues,
+    create: objectCreate,
+    defineProperty: defineOwnProperty,
+  } = Object;
+  const {
+    apply: call,
+    defineProperty: reflectDefineProperty,
+    setPrototypeOf: reflectSetPrototypeOf,
+  } = Reflect;
+  const proxyConstructor = Proxy;
+  const { add: weakSetAdd, has: weakSetHas } = WeakSet.prototype;
+  const propertyDescriptorRecords = new WeakSet();
+  const coercePropertyDescriptorValue = (P, V) => {
+    switch (P) {
+      case "configurable":
+      case "enumerable":
+      case "writable":
+        return !!V;
+      case "value":
+        return V;
+      case "get":
+        if (V !== undefined && typeof V !== "function") {
+          throw new TypeError(
+            "Piscēs: Getters must be callable.",
+          );
+        } else {
+          return V;
+        }
+      case "set":
+        if (V !== undefined && typeof V !== "function") {
+          throw new TypeError(
+            "Piscēs: Setters must be callable.",
+          );
+        } else {
+          return V;
+        }
+      default:
+        return V;
+    }
+  };
+  const propertyDescriptorProxyHandler = Object.freeze(
+    Object.assign(
+      Object.create(null),
+      {
+        defineProperty(O, P, Desc) {
+          if (
+            P === "configurable" || P === "enumerable" ||
+            P === "writable" || P === "value" ||
+            P === "get" || P === "set"
+          ) {
+            // P is a property descriptor attribute.
+            const desc = setPropertyValues(objectCreate(null), Desc);
+            if ("get" in desc || "set" in desc) {
+              // Desc is an accessor property descriptor.
+              throw new TypeError(
+                "Piscēs: Property descriptor attributes must be data properties.",
+              );
+            } else if ("value" in desc || !(P in O)) {
+              // Desc has a value or P does not already exist on O.
+              desc.value = coercePropertyDescriptorValue(
+                P,
+                desc.value,
+              );
+            } else {
+              // Desc is not an accessor property descriptor and has no
+              // value, but an existing value is present on O.
+              /* do nothing */
+            }
+            const isAccessorDescriptor = "get" === P || "set" === P ||
+              "get" in O || "set" in O;
+            const isDataDescriptor = "value" === P ||
+              "writable" === P ||
+              "value" in O || "writable" in O;
+            if (isAccessorDescriptor && isDataDescriptor) {
+              // Both accessor and data attributes will be present on O
+              // after defining P.
+              throw new TypeError(
+                "Piscēs: Property descriptors cannot specify both accessor and data attributes.",
+              );
+            } else {
+              // P can be safely defined on O.
+              return reflectDefineProperty(O, P, desc);
+            }
+          } else {
+            // P is not a property descriptor attribute.
+            return reflectDefineProperty(O, P, Desc);
+          }
+        },
+        setPrototypeOf(O, V) {
+          if (V !== null) {
+            // V is not the property descriptor prototype.
+            return false;
+          } else {
+            // V is the property descriptor prototype.
+            return reflectSetPrototypeOf(O, V);
+          }
+        },
+      },
+    ),
+  );
+
+  return {
+    isPropertyDescriptorRecord: ($) =>
+      call(weakSetHas, propertyDescriptorRecords, [$]),
+    toPropertyDescriptor: (Obj) => {
+      if (type(Obj) !== "object") {
+        // The provided value is not an object.
+        throw new TypeError(
+          `Piscēs: Cannot convert primitive to property descriptor: ${O}.`,
+        );
+      } else {
+        // The provided value is an object.
+        const desc = objectCreate(null);
+        if ("enumerable" in Obj) {
+          // An enumerable property is specified.
+          defineOwnProperty(desc, "enumerable", {
+            configurable: true,
+            enumerable: true,
+            value: !!Obj.enumerable,
+            writable: true,
+          });
+        } else {
+          // An enumerable property is not specified.
+          /* do nothing */
+        }
+        if ("configurable" in Obj) {
+          // A configurable property is specified.
+          defineOwnProperty(desc, "configurable", {
+            configurable: true,
+            enumerable: true,
+            value: !!Obj.configurable,
+            writable: true,
+          });
+        } else {
+          // A configurable property is not specified.
+          /* do nothing */
+        }
+        if ("value" in Obj) {
+          // A value property is specified.
+          defineOwnProperty(desc, "value", {
+            configurable: true,
+            enumerable: true,
+            value: Obj.value,
+            writable: true,
+          });
+        } else {
+          // A value property is not specified.
+          /* do nothing */
+        }
+        if ("writable" in Obj) {
+          // A writable property is specified.
+          defineOwnProperty(desc, "writable", {
+            configurable: true,
+            enumerable: true,
+            value: !!Obj.writable,
+            writable: true,
+          });
+        } else {
+          // A writable property is not specified.
+          /* do nothing */
+        }
+        if ("get" in Obj) {
+          // A get property is specified.
+          const getter = Obj.get;
+          if (getter !== UNDEFINED && typeof getter !== "function") {
+            // The getter is not callable.
+            throw new TypeError("Piscēs: Getters must be callable.");
+          } else {
+            // The getter is callable.
+            defineOwnProperty(desc, "get", {
+              configurable: true,
+              enumerable: true,
+              value: getter,
+              writable: true,
+            });
+          }
+        } else {
+          // A get property is not specified.
+          /* do nothing */
+        }
+        if ("set" in Obj) {
+          // A set property is specified.
+          const setter = Obj.set;
+          if (setter !== UNDEFINED && typeof setter !== "function") {
+            // The setter is not callable.
+            throw new TypeError("Piscēs: Setters must be callable.");
+          } else {
+            // The setter is callable.
+            defineOwnProperty(desc, "set", {
+              configurable: true,
+              enumerable: true,
+              value: setter,
+              writable: true,
+            });
+          }
+        } else {
+          // A set property is not specified.
+          /* do nothing */
+        }
+        if (
+          ("get" in desc || "set" in desc) &&
+          ("value" in desc || "writable" in desc)
+        ) {
+          // Both accessor and data attributes have been defined.
+          throw new TypeError(
+            "Piscēs: Property descriptors cannot specify both accessor and data attributes.",
+          );
+        } else {
+          // The property descriptor is valid.
+          const record = new proxyConstructor(
+            desc,
+            propertyDescriptorProxyHandler,
+          );
+          call(weakSetAdd, propertyDescriptorRecords, [record]);
+          return record;
+        }
+      }
+    },
+  };
+})();
+
 export const {
   /**
    * Returns the primitive value of the provided object per its