f# - 字符串不兼容

Question

不确定我是否在这里遗漏了什么，当我尝试打印 url 时它会抛出错误。

Error string is not compatible with Printf.TextWriteFormat

type Credentials = {clientId: string; clientSecret: string}

let credentials = {clientId = ""; clientSecret = ""; deviceId = ""; deviceToken = ""}
let host = "https://example.com?grant_type=token";
let url = String.Format("%s?&client_id=%s&client_secret=%s", host, credentials.clientId, credentials.clientSecret)

printf url

let request = WebRequest.Create(url)

编辑 请求 header 接受不起作用

    let request = WebRequest.Create(url)
    request.Method <- "POST"
    request.ContentType <- "application/x-www-form-urlencoded"
    //request.Headers.Set "Accept" "application/json;charset=UTF-8"
    request.ContentLength <- (int64)data.Length


request.Accept <- "application/json;charset=UTF-8" // doesnt' work either

Answer 1

printf的第一个参数表示的类型函数期望不是 string ，这是一个 TextWriterFormat<'T>它可以从带有格式说明符的文字字符串派生出来。这个派生是一个编译器特性。

因此，您可以通过添加带有字符串格式说明符的文字字符串来解决它:

printf "%s" url

对于最后一行，您可以使用 sprintf它返回字符串，而不是打印它:

let url = sprintf "%s?&client_id=%s&client_secret=%s&device_id=%s&device_token=%s" host credentials.clientId credentials.clientSecret credentials.deviceId credentials.deviceToken

编辑

此代码有效:

open System.Net

type Credentials = {clientId: string; clientSecret: string; deviceId: string; deviceToken: string}

let credentials = {clientId = "www.stackoverflow.com"; clientSecret = ""; deviceId = ""; deviceToken = ""}
let host = "https://example.com?grant_type=token";
let url = sprintf "%s?&client_id=%s&client_secret=%s" host credentials.clientId credentials.clientSecret

printf "%s" url

let request = WebRequest.Create(url)