prawn：Prawn::Graphics#line_width=

#!/usr/bin/env ruby

require "prawn"

pdf = Prawn::Document.new

p pdf.line_width

pdf.line_width = 5
p pdf.line_width

pdf.move_to [100, 100]
pdf.line_to [50, 50]
pdf.stroke

pdf.render_file(File.basename($0, ".rb") + ".pdf")

で、

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