Rewrote Jake Wharton's wrapper of SpannableStringBuilder in Kotlin

Truss.java

import android.text.SpannableStringBuilder
import android.text.Spanned.SPAN_INCLUSIVE_EXCLUSIVE
import java.util.ArrayDeque
import java.util.Deque

// https://gist.github.com/JakeWharton/11274467
public class Truss {

    private val builder: SpannableStringBuilder = SpannableStringBuilder()
    private val stack: Deque<Span> = ArrayDeque()

    fun append(string: String): Truss {
        builder.append(string)
        return this
    }

    fun append(charSequence: CharSequence): Truss {
        builder.append(charSequence)
        return this
    }

    fun append(char: Char): Truss {
        builder.append(char)
        return this
    }

    fun append(number: Int): Truss {
        builder.append("$number")
        return this
    }

    /** Starts {@code span} at the current position in the builder. */
    fun pushSpan(span: Any): Truss {
        stack.addLast(Span(builder.length, span))
        return this
    }

    /** End the most recently pushed span at the current position in the builder. */
    fun popSpan(): Truss {
        val span = stack.removeLast()
        builder.setSpan(span.span, span.start, builder.length, SPAN_INCLUSIVE_EXCLUSIVE)
        return this
    }

    /** Create the final {@link CharSequence}, popping any remaining spans. */
    fun build(): CharSequence {
        while (!stack.isEmpty()) {
            popSpan()
        }
        return builder
    }
}

private data class Span(val start: Int, val span: Any)