Created
July 19, 2024 10:22
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A simple libfmt-esque addition to the lua string library.
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| -- A simple string formatting function that supports named arguments. | |
| -- It is inspired by libfmt (https://github.com/fmtlib/fmt) and Python's str.format() method. | |
| ---@param input string The string to format. | |
| ---@vararg any The arguments to format the string with. | |
| ---@return string formatted The formatted string. | |
| local function fmt(input, ...) | |
| local args = { ... } | |
| local is_table_arg = type(args[1]) == "table" and #args == 1 | |
| local index = 1 | |
| local function replacer(key) | |
| if key == "" then | |
| key = tostring(index) | |
| index = index + 1 | |
| end | |
| local pattern, format_spec = key:match("([^:]*):?(.*)") | |
| if pattern == "" then | |
| key = tostring(index) .. key | |
| index = index + 1 | |
| pattern, format_spec = key:match("([^:]*):?(.*)") | |
| end | |
| local keys = {} | |
| for part in string.gmatch(pattern, "[^.]+") do | |
| table.insert(keys, part) | |
| end | |
| local value = is_table_arg and args[1] or args | |
| for _, part in ipairs(keys) do | |
| value = value[tonumber(part) or part] | |
| if type(value) ~= "table" then | |
| break | |
| end | |
| end | |
| if format_spec ~= "" and type(value) ~= "table" then | |
| value = string.format("%" .. format_spec, value) | |
| end | |
| return tostring(value) | |
| end | |
| return (input:gsub("{(.-)}", replacer)) | |
| end | |
| ---@param self string | |
| string.fmt = function(self, ...) | |
| return fmt(self, ...) | |
| end | |
| ---@param self string | |
| getmetatable("").__mod = function(self, ...) | |
| return fmt(self, ...) | |
| end | |
| ---@param self string | |
| getmetatable("").__call = function(self, ...) | |
| return fmt(self, ...) | |
| end | |
| return fmt |
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| local fmt = require "fmt" | |
| -- Basic positional arguments | |
| assert(string.fmt("{}, {}", 1, "foo"), "1, foo") | |
| -- Basic positional argument using % operator | |
| assert("{}" % "foo", "foo") | |
| -- Basic formatted positional argument using % operator | |
| assert("{:.2f}" % 1, "1.00") | |
| -- Basic positional arguments using call syntax | |
| assert(("{}, {}")(1, "foo"), "1, foo") | |
| -- Named arguments | |
| assert(string.fmt("{a}, {b}", { a = 1, b = "foo" }), "1, foo") | |
| -- Named formatted arguments | |
| assert(string.fmt("{a:.2f}, {b}", { a = 1, b = "foo" }), "1.00, foo") | |
| -- Nested named arguments | |
| assert(string.fmt("{a.z}, {b.y}", { a = { z = 1 }, b = { y = "foo" } }), "1, foo") | |
| -- Nested formatted named arguments | |
| assert(string.fmt("{a.z:.2f}, {b.y}", { a = { z = 1 }, b = { y = "foo" } }), "1.00, foo") | |
| -- Nested named positional arguments | |
| assert(string.fmt("{a.}, {a.}", { a = { 1, "foo"} }), "1, foo") | |
| -- Mixed positional and named arguments | |
| assert("{a}, {}, {b}, {}" % { a = 1, b = "foo", [1] = "baz", [2] = "bang" }, "1, baz, foo, bang") | |
| -- Mixed formatted positional and named arguments | |
| assert("{a:.2f}, {}, {b}, {}" % { a = 1, b = "foo", [1] = "baz", [2] = "bang" }, "1.00, baz, foo, bang") | |
| -- Named arguments using call syntax | |
| assert(("{a}, {b}"){ a = 1, b = "foo" }, "1, foo") | |
| -- Named formatted arguments using call syntax | |
| assert(("{a:.2f}, {b}"){ a = 1, b = "foo" }, "1.00, foo") | |
| -- Method syntax on string with positional arguments | |
| local test = "{}, {}" | |
| assert(test:fmt(1, "foo"), "1, foo") | |
| -- Method syntax on string with formatted positional arguments | |
| local test_fmt = "{:.2f}, {}" | |
| assert(test_fmt:fmt(1, "foo"), "1.00, foo") |
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