QIO

Managed

Managed is a special data structure that is built to provide certain guarantees around resources. It makes sure that,

  1. The resource is acquired only when an operation is ready to be performed.
  2. The resource is released when the operation is completed successfully.
  3. The resource is released when there is a failure.
  4. The resource is released when an operation is cancelled.

Creating Managed

You can create a managed resource using Managed.make.

+ import {Managed, QIO} from '@qio/core'
+ import {promises as fs} from 'fs'
+
+ const open = QIO.encaseP(fs.open)
+ const close = QIO.encaseP((fd: fs.FileHandle) => fd.close())
+
+ const managedFD = Managed.make(open('./abc.txt', 'w'), close)

Using Managed

managedFD can be used through the .use operator.

  import {Managed, QIO} from '@qio/core'
  import {promises as fs} from 'fs'

  const open = QIO.encaseP(fs.open)
  const close = QIO.encaseP((fd: fs.FileHandle) => fd.close())
  const write = QIO.encaseP((fd: fs.FileHandle, buffer: Buffer) =>
    fd.write(buffer)
  )
+ const write = QIO.encaseP((fd: fs.FileHandle, buffer: Buffer) =>
+   fd.write(buffer)
+ )

  const managedFD = Managed.make(open('./abc.txt', 'w'), close)

+ managedFD.use(fd => write(fd, Buffer.from('DATA')))
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