An adaptation of Truss from JakeWharton wrote in kotlin

KTruss.kt

import android.text.SpannableStringBuilder
import android.text.Spanned.SPAN_INCLUSIVE_EXCLUSIVE
import java.util.*

/** A [SpannableStringBuilder] wrapper whose API doesn't make me want to stab my eyes out.  */
class KTruss {
    private val builder: SpannableStringBuilder = SpannableStringBuilder()
    private val stack: Deque<Span> = ArrayDeque<Span>()

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

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

    fun append(c: Char): KTruss {
        builder.append(c)
        return this
    }

    fun append(number: Int): KTruss {
        builder.append(number.toString())
        return this
    }

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

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

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

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

Usage.markdown

#USAGE

val spanned = KTruss().append("text1").append(" ")
                    .pushSpan(ForegroundColorSpan(color(R.color.red)))
                    .pushSpan(StyleSpan(Typeface.BOLD))
                    .append("text2")
                    .popSpan()
                    .popSpan()
                    
textView.setText(spanned.build(), TextView.BufferType.SPANNABLE)

Add a popSpan() for each pushSpan() to finish whatever span, remember that is a queue then the first popSpan removes the last pushSpan() added.

##Result text1 text2[red]

Thanks for the straight port.

2 optimisations can be considered

1. we can join init with declarations

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

2. no need of data class for span

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