Design Patterns MCP Server

{ "id": "concat-map", "name": "ConcatMap Pattern", "category": "Reactive", "description": "Projects emissions to inner observables and concatenates results in order", "when_to_use": "Sequential processing\nOrder preservation\nDependent operations", "benefits": "Order preservation\nSequential processing\nPredictable results", "drawbacks": "Slower execution\nHead-of-line blocking\nResource queueing", "use_cases": "Sequential API calls\nFile uploads\nOrdered processing", "complexity": "Medium", "tags": [ "reactive", "concat", "sequential" ], "examples": { "typescript": { "language": "typescript", "code": "// ConcatMap: sequential inner observables\nclass Observable<T> {\n concatMap<R>(project: (value: T) => Observable<R>): Observable<R> {\n return new Observable(observer => {\n const queue: Array<() => void> = [];\n let activeInner = false;\n let outerCompleted = false;\n \n const processNext = () => {\n if (activeInner || queue.length === 0) {\n if (outerCompleted && queue.length === 0) {\n observer.complete();\n }\n return;\n }\n \n activeInner = true;\n queue.shift()!();\n };\n \n return this.subscribe({\n next: value => {\n queue.push(() => {\n project(value).subscribe({\n next: inner => observer.next(inner),\n error: err => observer.error(err),\n complete: () => {\n activeInner = false;\n processNext();\n }\n });\n });\n processNext();\n },\n error: err => observer.error(err),\n complete: () => {\n outerCompleted = true;\n processNext();\n }\n });\n });\n }\n}\n\n// Usage: Sequential async operations\nconst urls = from(['url1', 'url2', 'url3']);\n\nurls\n .concatMap(url => fetch(url)) // Wait for each to complete\n .subscribe({\n next: response => console.log('Response:', response),\n error: () => {},\n complete: () => {}\n });" } } }