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-rw-r--r--util/format.lua74
1 files changed, 74 insertions, 0 deletions
diff --git a/util/format.lua b/util/format.lua
new file mode 100644
index 00000000..5f2b12be
--- /dev/null
+++ b/util/format.lua
@@ -0,0 +1,74 @@
+--
+-- A string.format wrapper that gracefully handles invalid arguments
+--
+
+local tostring = tostring;
+local select = select;
+local assert = assert;
+local unpack = unpack;
+local type = type;
+
+local function format(format, ...)
+ local args, args_length = { ... }, select('#', ...);
+
+ -- format specifier spec:
+ -- 1. Start: '%%'
+ -- 2. Flags: '[%-%+ #0]'
+ -- 3. Width: '%d?%d?'
+ -- 4. Precision: '%.?%d?%d?'
+ -- 5. Option: '[cdiouxXaAeEfgGqs%%]'
+ --
+ -- The options c, d, E, e, f, g, G, i, o, u, X, and x all expect a number as argument, whereas q and s expect a string.
+ -- This function does not accept string values containing embedded zeros, except as arguments to the q option.
+ -- a and A are only in Lua 5.2+
+
+
+ -- process each format specifier
+ local i = 0;
+ format = format:gsub("%%[^cdiouxXaAeEfgGqs%%]*[cdiouxXaAeEfgGqs%%]", function(spec)
+ if spec ~= "%%" then
+ i = i + 1;
+ local arg = args[i];
+ if arg == nil then -- special handling for nil
+ arg = "<nil>"
+ args[i] = "<nil>";
+ end
+
+ local option = spec:sub(-1);
+ if option == "q" or option == "s" then -- arg should be string
+ args[i] = tostring(arg);
+ elseif type(arg) ~= "number" then -- arg isn't number as expected?
+ args[i] = tostring(arg);
+ spec = "[%s]";
+ end
+ end
+ return spec;
+ end);
+
+ -- process extra args
+ while i < args_length do
+ i = i + 1;
+ local arg = args[i];
+ if arg == nil then
+ args[i] = "<nil>";
+ else
+ args[i] = tostring(arg);
+ end
+ format = format .. " [%s]"
+ end
+
+ return format:format(unpack(args));
+end
+
+local function test()
+ assert(format("%s", "hello") == "hello");
+ assert(format("%s") == "<nil>");
+ assert(format("%s", true) == "true");
+ assert(format("%d", true) == "[true]");
+ assert(format("%%", true) == "% [true]");
+end
+
+return {
+ format = format;
+ test = test;
+};