string representing file path.
A promise of string read.
import std.file : write, remove; import dpromise.utils : runEventloop; write("hoge.txt", "hogehogepiyopiyo"); scope(exit) remove("hoge.txt"); readTextAsync("hoge.txt").then( (s) { assert(s == "hogehogepiyopiyo"); } ); runEventloop();
Read file path with asynchronous IO and return data read as a promise of string(validate with std.utf.validate)
If an error occurred, the promise will be rejected.