Object Patterns with Tables

Default Field

Choose a default when an object-style field is blank.

default field Object-style records often need defaults for missing or blank fields.

Default Field

explicit
default_field.lua
Replay: real traced execution (multi-file project)
local explicit = ""
local fallback = ({theme = "gray"}).theme
local theme = explicit
if theme == nil or theme == "" then
    theme = fallback
end
print("theme=" .. theme)

local explicit = "blue"
local fallback = ({theme = "gray"}).theme
local theme = explicit
if theme == nil or theme == "" then
    theme = fallback
end
print("theme=" .. theme)

local explicit = nil
local fallback = ({theme = "gray"}).theme
local theme = explicit
if theme == nil or theme == "" then
    theme = fallback
end
print("theme=" .. theme)

  1. explicit ← (empty), fallback ← gray, theme ← (empty)

    1local explicit→ (empty) = "" --@explicit="blue", nil2local fallback→ gray = ({theme = "gray"}).themegray3local theme→ (empty) = explicit(empty)4if theme == nil or theme == "" then

  2. theme ← gray

    3local theme = explicit4if theme(empty) == nil or theme == "" then5    theme→ gray = fallbackgray6end

  3. print("theme=" .. theme)

    6end7print("theme=" .. themegray)
    outputtheme=gray

  1. explicit ← blue, fallback ← gray, theme ← blue

    1local explicit→ blue = "blue"2local fallback→ gray = ({theme = "gray"}).themegray3local theme→ blue = explicitblue4if theme == nil or theme == "" then5    theme = fallback6end7print("theme=" .. themeblue)
    outputtheme=blue

  1. explicit ← nil, fallback ← gray, theme ← nil

    1local explicit→ nil = nil2local fallback→ gray = ({theme = "gray"}).themegray3local theme→ nil = explicitnil4if theme == nil or theme == "" then

  2. theme ← gray

    3local theme = explicit4if themenil == nil or theme == "" then5    theme→ gray = fallbackgray6end

  3. print("theme=" .. theme)

    6end7print("theme=" .. themegray)
    outputtheme=gray