Style templates with IES

Use the style template syntax inside Interpolated Expression Sequences (IES) to write colorized and formatted text to stdout, stderr, or any output range.

Template Syntax

Style blocks use the {styleName content} syntax, where styleName is one or more dot-separated terminal styles.

• Single Style: {red error} formats the text using a red foreground.
• Chained Styles: {bold.red critical} combines styles (bold and red foreground).
• Nested Blocks: {bold outer {red inner}} applies bold to the entire block, and red additionally to inner.
• Style Negation: Use ~ prefix to remove a style from the inherited set: {bold.red styled {~red plain}}.
• True-color & palette: {#cba6f7 mauve} (24-bit hex), {@183 palette} (256-color index); prefix with bg for the background ({bg#1e1e2e …}, {bg@235 …}).
• Underline shapes & color: {underline x} (single), plus {doubleUnderline …}, {curlyUnderline …}, {dottedUnderline …}, {dashedUnderline …}; set an independent underline color with {ul#ff5555 …} or {ul@N …}. Curly red underlines make good inline diagnostics: {curlyUnderline.ul#ff5555 typo}.
• Escaped Braces: Use #{ and #} to write literal braces: #{style#} outputs {style}.

All standard ANSI colors and formats (red, green, blue, cyan, yellow, magenta, white, black, bold, dim, italic, underline, inverse, strikethrough, hidden, bgRed, bgGreen, etc.) are supported.

Terminal color depth

Every entry point (styledText, plainText, writeStyled, styledWrite*, styled) accepts an optional leading ColorDepth argument. It folds 24-bit and 256-palette colors down to what the terminal can address — trueColor (the default) emits them verbatim, ansi256 folds RGB to the nearest palette entry, and ansi16 folds to the nearest classic color:

import sparkles.base.term_color : ColorDepth, detectColorDepth;

styledText(i"{#cba6f7 x}");                       // \x1b[38;2;203;166;247m…
styledText(ColorDepth.ansi256, i"{#cba6f7 x}");   // \x1b[38;5;183m…
styledText(ColorDepth.ansi16, i"{#cba6f7 x}");    // \x1b[37m…
styledText(detectColorDepth(), i"{#cba6f7 x}");   // fold to the real terminal

Write directly to stdout or stderr

Use the styledWrite* helpers to write styled IES content directly to standard output or error streams:

#!/usr/bin/env dub
/+ dub.sdl:
    name "base_style_text_templates"
    dependency "sparkles:base" version="*"
+/
import sparkles.base.styled_template : styledWriteln, styledWritelnErr;

void main()
{
    // Write styled text to stdout
    styledWriteln(i"Status: {green.bold OK} | Service: {cyan database}");

    // Write styled text to stderr
    styledWritelnErr(i"{red.bold Fatal Error: connection refused}");
}

Fatal Error: connection refused
Status: OK | Service: database

Convert to strings

Use styledText to evaluate an IES template and return a styled string containing ANSI escape codes. Use plainText to evaluate the IES but strip all style markup, returning a clean plain-text string:

#!/usr/bin/env dub
/+ dub.sdl:
    name "base_styled_text_conversion"
    dependency "sparkles:base" version="*"
+/
import std.stdio : writeln;
import sparkles.base.styled_template : styledText, plainText;

void main()
{
    auto template_ = i"Progress: {yellow 45%}";

    string styled = styledText(template_);
    string plain = plainText(template_);

    writeln("Styled length: ", styled.length); // includes escape characters
    writeln("Plain length: ", plain.length);   // plain text only
}

Styled length: 23
Plain length: 13

Format into custom buffers

For memory-conscious or @nogc formatting, use writeStyled to write formatted, styled templates into any Writer (such as a UniqueBuffer):

#!/usr/bin/env dub
/+ dub.sdl:
    name "base_write_styled_buffer"
    dependency "sparkles:base" version="*"
+/
import std.stdio : writeln;
import sparkles.base.buffer : UniqueBuffer;
import sparkles.base.styled_template : writeStyled;

void main()
{
    UniqueBuffer!(char, 128) buf;
    writeStyled(buf, i"Level: {magenta debug}");

    writeln(buf[]);
}

Level: debug