Tutorial: Module compat

This tutorial covers the following compat module API and its usage:

Listing options
Listing options details
Changing option value
Restoring defaults
Getting compat setup with compat.dump()
Setting all options to a specific value with compat.dump()
Adding an option during runtime

Listing options

The options list is serialized in the interactive console with additional details for user convenience:

All non-obsolete options in order new > old > default.
Serialization returns array-like table with tables {<option> = <value>}.
The result of compat serialization can still be indexed as a normal key-value table.

tarantool> compat = require('compat')
---
...

tarantool> compat
---
- - json_escape_forward_slash: new
- - option_2: old
- - option_default_old: default (old)
- - option_default_new: default (new)
...

Listing options details

current – the state of the option.
default – the default state of the option.
brief – text options description with a link to more detailed description.

tarantool> compat.option_default_new
---
- current: old
default: new
brief: <...>
...

Changing option value

You can do it directly, or by passing a table with option-value. Possible values to assign are ‘new’ , ‘old’, and ‘default’.

tarantool> compat.json_escape_forward_slash = 'old'
---
...

tarantool> compat{json_escape_forward_slash = 'new', option_2 = 'default'}
---
...

Restoring defaults

By setting ‘default’ value to an option:

tarantool> compat.option_2 = 'default'
---
...

tarantool> compat.option_2
---
- current: default
- default: new
- brief: <...>
...

Getting compat setup with compat.dump()

tarantool> compat({
         >     obsolete_set_explicitly = 'new',
         >     option_set_old = 'old',
         >     option_set_new = 'new'
         > })
---
...

tarantool> compat
---
- - option_set_old: old
- - option_set_new: new
- - option_default_old: default (old)
- - option_default_new: default (new)
...

# Obsolete options are not returned in serialization, but have the following values:
# - obsolete_option_default: default (new)
# - obsolete_set_explicitly: new

# nil does output obsolete unset options as 'default'
tarantool> compat.dump()
---
- require('compat')({
            option_set_old          = 'old',
            option_set_new          = 'new',
            option_default_old      = 'default',
            option_default_new      = 'default',
            obsolete_option_default = 'default', -- obsolete since X.Y
            obsolete_set_explicitly = 'new',     -- obsolete since X.Y
    })
...

# 'current' is the same as nil with default set to current values
tarantool> compat.dump('current')
---
- require('compat')({
            option_set_old          = 'old',
            option_set_new          = 'new',
            option_default_old      = 'old',
            option_default_new      = 'new',
            obsolete_option_default = 'new',     -- obsolete since X.Y
            obsolete_set_explicitly = 'new',     -- obsolete since X.Y
    })
...

# 'new' outputs obsolete as 'new'.
tarantool> compat.dump('new')
---
- require('compat')({
            option_set_old          = 'new',
            option_set_new          = 'new',
            option_default_old      = 'new',
            option_default_new      = 'new',
            obsolete_option_default = 'new',     -- obsolete since X.Y
            obsolete_set_explicitly = 'new',     -- obsolete since X.Y
    })
...

# 'old' outputs obsolete options as 'new'.
tarantool> compat.dump('old')
---
- require('compat')({
            option_set_old          = 'old',
            option_set_new          = 'old',
            option_default_old      = 'old',
            option_default_new      = 'old',
            obsolete_option_default = 'new',     -- obsolete since X.Y
            obsolete_set_explicitly = 'new',     -- obsolete since X.Y
    })
...

# 'default' does output obsolete options as default.
tarantool> dump('default')
---
- require('compat')({
            option_set_old          = 'default',
            option_set_new          = 'default',
            option_default_old      = 'default',
            option_default_new      = 'default',
            obsolete_option_default = 'default', -- obsoleted since X.Y
            obsolete_set_explicitly = 'default', -- obsoleted since X.Y
    })
...

Setting all options to a specific value with compat.dump()

use compat.dump() to get a specific configuration
copy and paste it into console (or use loadstring())

tarantool> compat.dump('new')
---
- require('compat')({
      option_2 = 'new',
      json_escape_forward_slash = 'new',
  })
...
tarantool> require('compat')({
      option_2 = 'new',
      json_escape_forward_slash = 'new',
  })
---
...

tarantool> compat
---
- - json_escape_forward_slash: new
- - option_2: new
...

Adding an option during runtime

User must provide a table with:

name (string)
default (’new’ / ’old’)
brief (explanation of the option, can be multiline string)
obsolete (’X.Y’ / nil) — tarantool version that marked option as obsolete. When nil, option is treated as non-obsolete)
action function (argument - boolean is_new, changes the behavior accordingly)
run_action_now (true / false / nil) if add_options should run action afterwards, false by default

Option hot reload:

You can change an existing option in runtime using add_option(), it will update all the fields but keep currently selected behavior if any. The new action will be called afterwards.

tarantool> compat.add_option{
                 name = 'option_4',
                 default = 'new',
                 brief = "<...>",
                 obsolete = nil,          -- you can explicitly mark the option as non-obsolete
                 action = function(is_new)
                      print(("option_4 action was called with is_new = %s!"):format(is_new))
                 end,
                 run_action_now = true
           }
option_4 postaction was called with is_new = true!
---
...

tarantool> compat.add_option{             -- hot reload of option_4
                 name = 'option_4',
                 default = 'old',         -- different default
                 brief = "<...>",
                 action = function(is_new)
                      print(("new option_4 action was called with is_new = %s!"):format(is_new))
                 end
           }
---
...         -- action is not called by default

Version: