天之书-InjectFlags，谁懂我服

injectArgs这是angular种依赖注入代码摘录，看了半天，始终没有头绪,脑袋不够用了!感觉整个人都不好了!

export const enum InjectFlags {
    Default = 0 << 0, // 0b0000
    Host = 1 << 0, // 0b0001
    Self = 1 << 1, // 0b0010
    SkipSelf = 1 << 2, // 0b0100
    Optional = 1 << 3, // 0b1000 
}

@Default() 0b0000 * @Host() 0b0001 * @Self() 0b0010 * @SkipSelf() 0b0100 * @Optional() 0b1000 = 0b1111 4个二进制第一位标示Host是否开启，二位表示Self是否开启，三位表示SkipSelf是否开启,4位表示Optional是否开启。

// 这样的代码跟天数有啥区别
export function injectArgs(
    types: (Type<any> | InjectionToken<any> | any[])[]
): any[] {
    const args: any[] = [];
    for (let i = 0; i < types.length; i++) {
        const arg = types[i];
        if (Array.isArray(arg)) {
            if (arg.length === 0) {
                throw new Error('Arguments array must have arguments.');
            }
            let type: Type<any> | undefined = undefined;
            let flags: InjectFlags = InjectFlags.Default;
            for (let j = 0; j < arg.length; j++) {
                const meta = arg[j];
                if (meta instanceof Optional || meta.ngMetadataName === 'Optional') {
                    flags |= InjectFlags.Optional;
                } else if (meta instanceof SkipSelf || meta.ngMetadataName === 'SkipSelf') {
                    flags |= InjectFlags.SkipSelf;
                } else if (meta instanceof Self || meta.ngMetadataName === 'Self') {
                    flags |= InjectFlags.Self;
                } else if (meta instanceof Inject) {
                    type = meta.token;
                } else {
                    type = meta;
                }
            }
            args.push(inject(type!, flags));
        } else {
            args.push(inject(arg));
        }
    }
    return args;
}

export const enum OptionFlags {
    Optional = 1 << 0, // 0b0001
    CheckSelf = 1 << 1, // 0b0010
    CheckParent = 1 << 2, // 0b0100
    Default = CheckSelf | CheckParent // 0b0110
}

@Optional & @Optional 不为0，其余均为0 @CheckSelf & @CheckSelf 和 @CheckSelf & @Default 不为0，其余均为0 @CheckParent & @CheckParent 和 @CheckParent & @Default 不为0，其余均为0 @Default & @Optional 为0，其余不为0

InjectFlags各个值&的话，只有自身与自身结果为正，其余均为0.

// 根据token解析出value
function resolveToken(
    token: any,
    record: Record | undefined,
    records: Map<any, Record>,
    parent: Injector,
    notFoundValue: any,
    flags: InjectFlags
): any {
    let value;
    // 没有SkipSelf
    if (record && !(flags & InjectFlags.SkipSelf)) {
        value = record.value;
        // circular
        if (value == CIRCULAR) {
            throw Error(NO_NEW_LINE + 'Circular dependency');
        } else if (value === EMPTY) { // empty
            record.value = CIRCULAR;
            let obj = undefined;
            let useNew = record.useNew;
            let fn = record.fn;
            let depRecords = record.deps;
            let deps = EMPTY;
            if (depRecords.length) {
                deps = [];
                for (let i = 0; i < depRecords.length; i++) {
                    const depRecord: DependencyRecord = depRecords[i];
                    const options = depRecord.options;
                    const childRecord =
                        // 如果是options = Default|CheckSelf
                        options & OptionFlags.CheckSelf ?
                            records.get(depRecord.token) : undefined;
                    deps.push(
                        // 递归
                        tryResolveToken(
                            depRecord.token,
                            childRecord,
                            records,
                            // childRecord && options != Default|CheckParent
                            !childRecord && !(options & OptionFlags.CheckParent) ? NULL_INJECTOR : parent,
                            // options == Default|Optional
                            options & OptionFlags.Optional ? null : Injector.THROW_IF_NOT_FOUND,
                            InjectFlags.Default
                        )
                    );
                }
            }
            record.value = value = useNew ? new (fn as any)(...deps) : fn.apply(obj, deps);
        }
    } else if (!(flags & InjectFlags.Self)) {
        // 获取上级
        value = parent.get(
            token,
            notFoundValue,
            InjectFlags.Default
        );
    }
    return value;
}

// 计算deps
function computeDeps(provider: StaticProvider): DependencyRecord[] {
    let deps: DependencyRecord[] = EMPTY;
    const providerDeps: any[] =
        (provider as ExistingProvider & StaticClassProvider & ConstructorProvider).deps;
    if (providerDeps && providerDeps.length) {
        deps = [];
        for (let i = 0; i < providerDeps.length; i++) {
            let options = OptionFlags.Default;
            let token = resolveForwardRef(providerDeps[i]);
            if (token instanceof Array) {
                for (let j = 0, annotations = token; j < annotations.length; j++) {
                    const annotation = annotations[j];
                    if (annotation instanceof Optional || annotation == Optional) {
                        options = options | OptionFlags.Optional;
                    } else if (annotation instanceof SkipSelf || annotation == SkipSelf) {
                        // 按位取反运算符 (~)
                        options = options & ~OptionFlags.CheckSelf;
                    } else if (annotation instanceof Self || annotation == Self) {
                        // 按位取反运算符 (~)
                        options = options & ~OptionFlags.CheckParent;
                    } else if (annotation instanceof Inject) {
                        token = (annotation as Inject).token;
                    } else {
                        token = resolveForwardRef(annotation);
                    }
                }
            }
            deps.push({ token, options });
        }
    } else if ((provider as ExistingProvider).useExisting) {
        const token = resolveForwardRef((provider as ExistingProvider).useExisting);
        deps = [{ token, options: OptionFlags.Default }];
    } else if (!providerDeps && !(USE_VALUE in provider)) {
        throw staticError('\'deps\' required', provider);
    }
    return deps;
}

我给你跪了！都是什么鬼!