2022年06月08日 日更 123/ 100 天

01. 今天接着来看，函数的骚操作。不使用 switch 实现状态机代码。我们先用 switch 实现，然后使用函数实现，两厢对比着学习一下。

02.先看 switch 的实现代码

/* 使用枚举传递状态 */enum TextProcessingMode {    Text,    Marker,    Code}class TextProcessor {    private mode: TextProcessingMode = TextProcessingMode.Text;    private result: string[] = [];    private codeSample: string[] = [];    processText(lines: string[]): string[] {        this.result = [];        this.mode = TextProcessingMode.Text;        for(let line of lines) {            this.processLine(line);        }        return this.result;    }    private processLine(line: string): void {        switch(this.mode) {            case TextProcessingMode.Text:                this.processTextLine(line);                break;            case TextProcessingMode.Marker:                this.processMarkerLine(line);                break;            case TextProcessingMode.Code:                this.processCodeLine(line);                break;        }    }    private processTextLine(line: string): void {        this.result.push(line);        if(line.startsWith("<!--")) {            this.loadCodeSample(line);            this.mode = TextProcessingMode.Marker;        }    }    private processMarkerLine(line: string): void {        this.result.push(line);        if(line.startsWith("```ts")) {            this.result =  this.result.concat(this.codeSample);            this.mode = TextProcessingMode.Code;        }    }    private processCodeLine(line: string): void {        if(line.startsWith("```")) {            this.result.push(line);            this.mode = TextProcessingMode.Text;        }    }    private loadCodeSample(line: string){        /** */    }}

03. 函数实现

class TextProcessor {    private result: string[] = [];    private processLine: (line: string) => void = this.processTextLine;    private codeSample: string[] = [];    processText(lines: string[]): string[] {        this.result = [];        this.processLine = this.processTextLine;        for (const line of lines) {            this.processLine(line);        }        return this.result;    }    private processTextLine(line: string): void {        this.result.push(line);        if(line.startsWith("<!--")) {            this.loadCodeSample(line);            this.processLine = this.processMarkerLine;        }    }    private processMarkerLine(line: string): void {        this.result.push(line);        if(line.startsWith("```ts")) {            this.result = this.result.concat(this.codeSample);            this.processLine = this.processCodeLine;        }    }    private processCodeLine(line: string): void {        if(line.startsWith("```")) {            this.result.push(line);            this.processLine = this.processTextLine;        }    }    private loadCodeSample(line: string) {        /** */    }}

04. 比较函数式实现和普通 switch 实现两种方式。函数式实现时，省略了状态转移的属性传递，在实现同样功能上，函数式的代码更少。所以，能用函数式实现的地方，统统使用函数式吧。

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