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File system composite

Treat files and folders through one interface so nested file-system structures can be processed uniformly.

Problem

A file system must support operations over both individual files and nested folders without forcing clients to handle leaf and container types through separate traversal logic.

Related patterns

Composite

View pattern →

Implementations

Composite

TypeScriptApplication

Composite in TypeScript

Represents files and folders through one interface so callers can calculate the size of an individual file or an entire directory tree uniformly.

TypeScript
interface FileSystemNode {
  getName(): string;
  getSizeInBytes(): number;
}

class FileNode implements FileSystemNode {
  constructor(
    private readonly name: string,
    private readonly sizeInBytes: number,
  ) {}

  getName() {
    return this.name;
  }

  getSizeInBytes() {
    return this.sizeInBytes;
  }
}

class FolderNode implements FileSystemNode {
  private readonly children: FileSystemNode[] = [];

  constructor(private readonly name: string) {}

  getName() {
    return this.name;
  }

  add(child: FileSystemNode) {
    this.children.push(child);
  }

  getSizeInBytes() {
    return this.children.reduce(
      (total, child) => total + child.getSizeInBytes(),
      0,
    );
  }
}

const invoices = new FolderNode("invoices");
invoices.add(new FileNode("january.pdf", 120_000));
invoices.add(new FileNode("february.pdf", 140_000));

const archive = new FolderNode("archive");
archive.add(invoices);
archive.add(new FileNode("readme.txt", 2_000));

console.log(archive.getSizeInBytes());

Associated technologies